Pokemon Red, Blue, and Yellow In-Game Tiers Reboot - Writeups

[DrumstickGaming]

Introduction
Welcome to the Pokémon Red, Blue, and Yellow in-game tier list! The goal of this list is to rank every Pokémon in Kanto in one of the six tiers, from S to E, each vaguely determining its viability. The major factor under which each is ranked is efficiency; a Pokémon that is efficient provides faster and easier solutions to major battles, which include Gym Leaders, Elite Four members, and the Champion at the Pokémon League, than ones that are inefficient. Pokémon in higher ranks, such as S and A, are considered very efficient, while those in lower tiers, such as D and E, are considered not very efficient.

What are the tiers?
There are 6 tiers in this list:

• S-tier
• A-tier
• B-tier
• C-tier
• D-tier
• E-tier

Why is a Pokémon in a certain tier?
Pokémon are ranked under the following five factors:

• Availability: This is how early a Pokémon becomes available in the game and how hard it is to find (read: encounter rate). Does it require significant backtracking, require HM moves, or just have a low encounter rate? This includes catching Water-types post-Surf.
• Typing: A Pokémon's typing can be of great importance for an efficient playthrough. How do the typing's matchups work against the entire game? If a Pokémon has better typing, it is often considered a higher rank.
• Stats: A Pokémon's stat distribution is crucial for its success. Does the Pokémon have a stat distribution that complements its movepool and typing? If a Pokémon has a stat distribution that favors both its typing and movepool, it will often be higher on the tier list. In general, a Pokémon with low Speed will often be ranked lower.
• Movepool: A Pokémon's movepool (both level-up and TM/HM) is crucial. What moves does the Pokémon naturally get and can possibly obtain? In general, a Pokemon will rank lower if it's reliant on contested TMs (such as Dig and Body Slam) to perform well. Furthermore, the Hyper Beam TM was not considered for any Pokemon's viability, because the TM takes a lot of money and time to be obtained.
• Major Battles: Major battles consist of Gym Leaders, the Elite 4, and the final battle with the Champion. How does the Pokémon contribute to these battles? A Pokémon that contributes to many major battles will often be seen higher than those that do not.

What tools is the player allowed to use?
The player is allowed to use almost any legitimate means within the cartridge for completing the game efficiently. The player is only allowed to trade to evolve Pokémon and not to receive outside help otherwise. The player is allowed to use items such as Potions, TMs, and Berries. X items are excluded from this list due to X Accuracy + OHKO moves being outlawed; X Items outside of X Accuracy were excluded for consistency reasons. Keep in mind that items have opportunity costs associated with them and can negatively contribute to a Pokémon's rank if it requires a multitude of items, such as two or more.

Writeup Format:

Availability:
Typing:
Stats:
Movepool:
Major Battles:
Additional Comments:

 

[DrumstickGaming]

S-Tier: The following Pokemon have the highest levels of efficiency. These Pokemon do not come very late, are very good as soon as you obtain them and OHKO or 2HKO most opponents effortlessly.

S-Tier

Abra

Availability: Early-game (Route 24, levels 8, 10, and 12 (RB), Route 5, level 7 (Y)).
Typing: Psychic is only resisted by Sabrina and neutral at worst against the other major opponents.
Stats: The Abra line boasts some of the highest Special and Speed stats in all of Gen 1, with less than a handful of the dex outspeeding them. The line have notably high critical hit chances (over 20%), but they are physically frail.
Movepool: Once Abra evolves into Kadabra at level 16, Confusion carries it to Psybeam and Psychic at levels 27 and 38 respectively. Recover at level 31 and Reflect at level 42 (or through TM) round out its moveset, with Seismic Toss and Thunder Wave providing situational use via TMs.
Major Battles: Kadabra and Alakazam excel in almost every major battle with STAB alone. There are a few exceptions where they have to use unorthodox tactics such as Misty and Sabrina necessitating Seismic Toss and Thunder Wave. Lance is the line's only true bad matchup, as Hyper Beam hits too hard and his Pokemon are too bulky to OHKO with Psychic, though Reflect and Recover can prove useful there.
Additional Comments: Overall, Abra is the most self-sufficient Pokemon in Pokemon Red, Blue and Yellow. Unlike most of the Pokedex, it needs very few TMs to sweep the game, very little babying to evolve to Kadabra, and can even overcome rare resists with a 30% chance to drop Special with Psychic. Even if you cannot evolve Kadabra into Alakazam, it will still perform excellently.

Clefairy

Availability: Early-game (Mt. Moon, levels 8-12 (RB), 9-13 (Y)),
Typing: Normal gives it a neutral matchup against every major trainer bar Agatha's Ghost-types and Bruno's Fighting-types.
Stats: Clefairy has well rounded stats except for a rather low Speed, but it's enough for most of the game.
Movepool: Clefable's level-up movepool is poor, but Clefairy's Sing at Lv13 is a decent support move. Clefable has access to the Mega Punch and Mega Kick TMs, whose power is augmented thanks to STAB. It has access to many special TMs such as Thunderbolt, Psychic, Ice Beam, and Blizzard to target weaknesses. Finally, it can learn Thunder Wave or Reflect.
Major Battles: Misty's Starmie can be defeated by Mega Punch or Seismic Toss. With STAB moves, Clefairy is capable of OHKOing and 2HKOing a lot of opponents, with its special coverage handling everything else.
Additional Comments: Clefairy can evolve almost immediately with the Moon Stone available at Mt. Moon. It can also wait until lv13 to learn Sing. Because of this, it requires minimal, if any, effort to reach its maximum potential through the whole game.

Drowzee

Availability: Early-game (Route 11, levels 9, 11, 13, and 15 (RB), 15, 17, 19 (Y)).
Typing: Psychic is only resisted by Sabrina and neutral at worst against the other major opponents.
Stats: The Drowzee line boasts average stats all-around aside from high Special.
Movepool: Drowzee starts with Hypnosis and learns Confusion at level 17 which carries it to Psychic at level 37. Pound upgrades to Headbutt (at level 24) and possibly to Body Slam / Tri Attack through TMs. Dream Eater via TM can be useful for healing after putting foes to sleep.
Major Battles: Drowzee can use Seismic Toss to get past Misty and Lt. Surge is decimated if you have Hypno by that point. Otherwise, Hypno has a good showing in all major battles with its Psychic / Normal coverage. The only slight stumble it faces is the Pokemon League, where its relatively sluggish Speed and average stats hinder it; however, this does not stop it from taking out at least a few Pokemon there.
Additional Comments: Other than a tiny slow period before Confusion, Drowzee is a great option for Pokemon Red, Blue and Yellow, with little TM reliance and helpful sleep access.

Jynx

Availability: Mid-game (trade for Poliwhirl (generally caught with Super Rod) in the house next to the Pokémon Center in Cerulean City) (RB).
Typing: Ice / Psychic is an outstanding offensive typing, with Ice hitting Dragon, Flying, Grass, and Ground types and Psychic hitting everything else neutrally aside from other Psychics; this means no Pokemon in RBY resists Jynx's STAB combination.
Stats: 95 Special and Speed are great for sweeping, but Jynx has poor physical stats and HP in return.
Movepool: Aside from Lovely Kiss for status, Ice Punch at level 31 is Jynx's only notable level-up move, with Blizzard via TM being a more powerful alternative for Ice STAB. Jynx must be taught the Psychic TM for STAB. Bubble Beam and Seismic Toss are other options, albeit unnecessary ones.
Major Battles: Jynx decimates most of the available opponents with STAB moves, with Lovely Kiss helping Jynx handle opponents like Blaine and Lorelei that are not weak to Jynx.
Additional Comments: While it comes relatively late and wants a TM for secondary STAB, Jynx is ruthlessly effective with trade bonus EXP and tears apart the second half of the game almost singlehandedly.

Mr. Mime

Availability: Early-game (trade an Abra (RB) or a Clefairy (Y) in a house on Route 2).
Typing: Psychic is only resisted by Sabrina and neutral at worst against the other major opponents.
Stats: Mr. Mime has a good Special and is relatively fast, having a 17.59% chance of landing a critical hit. However, it has low HP and Defense.
Movepool: Confusion upgrades to Psychic through TMs and Mr. Mime can also be given the Thunderbolt TM to improve the Lorelei matchup. Thunder Wave + Seismic Toss are Mr. Mime's best way of dealing with other Psychic-types. Support moves include Barrier, Light Screen at level 23, and Substitute at level 47, while Confusion can be kept as a secondary STAB to not waste Psychic's PP.
Major Battles: Psychic STAB is excellent for most matchups, with only Psychic-types requiring Thunderbolt or Seismic Toss to be defeated.
Additional Comments: Mr. Mime's early arrival, typing, offensive stats, and traded experience make it an all-around solid choice for any efficient run of the games.

Nidoran-F

Availability: Early-game (Route 22, levels 3-4 (R), 2-4 (B), or 2 or 4 (Y)).
Typing: Outside of worsening the matchup against Misty, Sabrina, and Lorelei, Poison / Ground is excellent, because it gives Nidoqueen a type advantage against Lt. Surge, RB Koga, Blaine, and Agatha, while also providing it with a handy immunity to poisoning.
Stats: Nidoqueen's stats are all around good; it can reasonably outspeed most of the opponents and can run mixed sets viably.
Movepool: Nidoqueen learns a variety of TMs, with Earthquake and Surf being the only ones that are really needed. Other TMs include Seismic Toss, Thunderbolt, Ice Beam, Blizzard, Water Gun, and Bubble Beam. Level-up wise, Nidoran-F learns Double Kick at level 12 in Yellow and Nidoqueen learns Body Slam at level 23.
Major Battles: Nidoqueen performs well in most matchups just with Earthquake and Surf, with Misty and Lorelei being the only opponents that really trouble it. In Yellow, it is also good for Brock due to learning Double Kick earlier. Other TMs can ease some matchups for Nidoqueen, but are generally not needed for a great performance.
Additional Comments: Early arrival and excellent major battles with just Earthquake and Surf, while also not needing other TMs to perform well, make Nidoran-F one of the best options for an efficient run of Pokémon Red, Blue, and Yellow. Evolve with Moon Stone as soon as possible, as Nidorina doesn't learn anything useful by level. In Red and Blue, you can also trade a Nidoran-M or Nidorino for a Nidoran-F or Nidorina in the Underground between Route 5 and 6 and Route 11, respectively. Note that Nidoqueen does not learn Dig in RBY.

Nidoran-M

Availability: Early-game (Route 22, levels 2-4 (R), 3-4 (B), or 2 or 4 (Y)).
Typing: Outside of worsening the matchup against Misty, Sabrina, and Lorelei, Poison / Ground is excellent, because it gives Nidoking a type advantage against Lt. Surge, RB Koga, Blaine, and Agatha, while also providing it with a handy immunity to poisoning.
Stats: Nidoking's stats are all around good; it can reasonably outspeed most of the opponents and can run mixed sets viably.
Movepool: Nidoking learns a variety of TMs, with Earthquake and Surf being the only ones that are really needed. Other TMs include Seismic Toss, Thunderbolt, Ice Beam, Blizzard, Water Gun, and Bubble Beam. Level-up wise, Nidoran-M learns Horn Attack at level 8 and, in Yellow, Double Kick at level 12, and Nidoking learns Thrash at level 23.
Major Battles: Nidoking performs well in most matchups just with Earthquake and Surf, with Misty and Lorelei being the only opponents that really trouble it. In Yellow, it is also good for Brock due to learning Double Kick earlier. Other TMs can ease some matchups for Nidoking, but are generally not needed for a great performance.
Additional Comments: Early arrival and excellent major battles with just Earthquake and Surf, while also not needing other TMs to perform well, make Nidoran-M one of the best options for an efficient run of Pokémon Red, Blue, and Yellow. Evolve with Moon Stone as soon as possible, as Nidorino doesn't learn anything useful by level. Note that Nidoking does not learn Dig in RBY.

 

[DrumstickGaming]

A-Tier: The following Pokemon are also very efficient, but fail to reach the level of S-tier, typically because they come slightly later, do not claim enough OHKOs or 2HKOs or need a relative amount of time in order to become good.

A-Tier

Articuno

Availability: Late-game (Seafoam Islands, level 50).
Typing: Ice / Flying provides good matchups against Giovanni, Bruno, and Lance, with everyone else save for Blaine being neutral.
Stats: 125 Special, 100 Defense and good other stats make Articuno a bulky yet somewhat fast sweeper.
Movepool: Starts with Ice Beam and Peck, learning Blizzard at level 51. Fly via HM and Toxic and BubbleBeam via TMs provide other options.
Major Battles: Stomps every major battle left save for Blaine and Lorelei due to its high level and almost nothing resisting Ice STAB. You can take out most of Blaine's team (though it's slightly harder in Yellow due to Flamethrower and higher levels) and Fly + Toxic can handle Lorelei if needed. Mimic also has a situational use against Lorelei to choose Slowbro's Amnesia to boost up and muscle through with STAB.
Additional Comments: Articuno is a fantastic option for stomping the last third of Pokemon Red, Blue and Yellow. However, its biggest flaws are the reliance on the Master Ball to be obtained quickly and Seafoam Islands being out of the way. Blizzard's 90% accuracy in Red, Blue and Yellow makes it far more reliable than in later generations, though it does have 5 PP.

Diglett

Availability: Early-game (Diglett's Cave, levels 15-22).
Typing: Ground typing gives Dugtrio an advantage against Lt. Surge, Giovanni, Blaine and Agatha while being weak to Misty, Erika, and Lorelei.
Stats: A fantastic 120 base Speed and decent base 80 Attack combined with a 23.44% critical hit rate as Dugtrio are good for sweeping, though it is very frail.
Movepool: Dig upon capture serves as Dugtrio's main STAB, with Slash at level 35 providing guaranteed critical hits when used. Earthquake is learned naturally at level 47, though it is the same base power as Dig in Pokemon Red, Blue and Yellow. Rock Slide can be taught via TM.
Major Battles: Obliterates Lt. Surge and loses to Erika and Lorelei, but is good for almost everyone else, particularly Koga, Blaine, Giovanni, and Agatha.
Additional Comments: A level 29 or 31 Dugtrio can be found in Diglett's Cave at a 5% rate (easier with Repel and a level 23+ Pokemon) but aside from the higher level, it performs basically the same as just catching a Diglett (not to mention Dugtrio is hard to catch). Diglett is a low investment Pokemon with its fragility being its biggest flaw.

Doduo

Availability: Mid-game (Route 16. requires Cut).
Typing: Normal / Flying typing gives Dodrio advantages against Erika and Bruno's Fighting types, though it is neutral elsewhere save for bad matchups against Lorelei and Rock / Ground types.
Stats: Dodrio has high Attack and Speed and a 19.53% chance to land critical hits, though its defenses are low.
Movepool: Doduo can be taught Fly via HM and Tri Attack via TM to get it by until Drill Peck at level 31. Hyper Beam via TM can prove useful, but Dodrio will need to OHKO with it to not be left vulnerable and it takes some time to buy the 5,500 coins needed from the Game Corner.
Major Battles: Great for Erika and Bruno, but generally average elsewhere aside from having the Speed to potentially outpace and Drill Peck Agatha's team. Bad for Lorelei and Lance as their mons can take a hit and retaliate for heavy damage on Dodrio,
Additional Comments: Dodrio is a great Pokemon, but it will generally need Hyper Beam as a finishing move frequently end-game.

Eevee (Vaporeon)

Availability: Mid-game (Celadon Mansion top floor as a level 25 Eevee).
Typing: Pure Water typing makes Vaporeon good against Blaine and Giovanni but bad for Erika and Lorelei, being neutral everywhere else.
Stats: High HP and Special make Vaporeon a great Special tank, though its physical stats and Speed are somewhat lacking.
Movepool: BubbleBeam via TM gets Vaporeon by until Surf, with Acid Armor at level 42 (RB) or level 47 (Y) helping against Lance. Otherwise, only Ice Beam (or Blizzard later) via TM are needed to be effective against Erika and Lance.
Major Battles: Vaporeon can perform decently against Erika with Ice Beam, but it won't sweep her. Otherwise, Surf spam performs good against the remaining bosses aside from Sabrina, Lorelei, and Agatha (due to their Pokemon with high Special and resistances in Lorelei's case).
Additional Comments: A Water Stone to evolve Eevee can immediately be obtained from the Celadon Dept. Store. Due to its ease of use, Vaporeon is one of the best Water types in Pokemon Red, Blue, and Yellow.

Gastly

Availability: Mid-game (Pokemon Tower).
Typing: Ghost / Poison typing gives the Gastly line immunities to Normal and Fighting moves as well as Bug, Poison, and Grass resistances, which help against Erika, Koga, and Bruno. Sabrina and Giovanni (in Viridian Gym in Yellow) hits the line super-effectively, however.
Stats: Fantastic Special and Speed make Haunter and Gengar good special sweepers with a roughly 20% critical hit rate, though their physical stats and HP are very low.
Movepool: Haunter and Gengar greatly benefit from the Psychic TM (with Dream Eater as an alternative), though they can also be taught the Thunderbolt and Mega Drain TMs for coverage. Night Shade can also prove useful against foes with high Special occasionally, and Hypnosis at level 29 can put foes to sleep, which works well with Dream Eater at level 38 if needed.
Major Battles: Psychic lets Haunter and Gengar decimate Erika, Koga, and Bruno, with Night Shade helping against Sabrina. Giovanni is dealt with through Mega Drain and Psychic, with Mega Drain / Thunderbolt helping against Lorelei. Psychic is useful for Agatha, but Haunter and Gengar are average elsewhere.
Additional Comments: Haunter and Gengar are good Special sweepers, though they will need a TM or two to be effective. Haunter and Gengar perform roughly the same, though Haunter is slightly more reliant on Hypnosis due to its lower power and bulk.

Sandshrew

Availability: Early-game (Route 4 (RB); Route 3 (Y).
Typing: Ground typing gives Sandslash advantages against several major battles while only being weak to a few others.
Stats: Good physical stats with roughly average HP and Speed make Sandslash a good physical tank, though it must be wary of Special moves. Also, Sandslash is fast enough to always land a critical hit with Slash at 65 base Speed.
Movepool: Slash at level 17, Dig through TM, and Rock Slide via TM in the Celadon Dept. Store are all Sandslash needs to be effective, though Swords Dance via TM can also help boost Ground STAB.
Major Battles: Loses to Misty, Erika, and Lorelei, but is good for almost everyone else, particularly Lt. Surge, Koga, Blaine, Giovanni, and Agatha.
Additional Comments: A combination of an early evolution, minimal investment, and few outright bad matchups make Sandshrew a good choice.

Squirtle (RB)

Availability: Early-game (Pallet Town, starter).
Typing: Water typing gives it an edge against Brock, Blaine, and Giovanni, while giving Squirtle a weakness to Lt. Surge and Erika.
Stats: Squirtle has good well-rounded stats with an emphasis on Defense.
Movepool: Bubble upgrades to Water Gun and then BubbleBeam via TM, with Surf later on via HM. Coverage options in the form of Mega Punch, Dig, and Ice Beam / Blizzard exist, but only an Ice move is really necessary. Seismic Toss helps against Misty while Strength serves as a more accurate Mega Punch replacement.
Major Battles: Squirtle does well in most major battles with only Erika, Sabrina, Lorelei and Agatha giving it trouble. Squirtle has advantages against Brock, Misty, Blaine, Giovanni, Bruno, and Lance in return, performing neutrally elsewhere.
Additional Comments: Squirtle is by far the best of the the starters with a self-sufficient movepool that is only held back by a couple of bad matchups.

Zapdos

Availability: Late-game (Power Plant, level 50).
Typing: Electric / Flying makes Zapdos good for Lorelei, Bruno, and some of Lance, with everywhere else being neutral matchups. It struggles against Rock / Ground types though.
Stats: Fantastic Special and Speed and great other stats make Zapdos an extremely competent sweeper with a 19.53% critical hit rate.
Movepool: Starts with Drill Peck and Thundershock, learning Thunder at level 51. Thunderbolt via TM will be Zapdos's most reliable attack though.
Major Battles: Stomps pretty much every major battle left if given Thunderbolt due to its high level of 50 when obtained. Drill Peck handles Sabrina, Agatha, and Bruno's Fighting types.
Additional Comments: Zapdos is a fantastic option for stomping the last third of Red, Blue and Yellow. However, its biggest flaws are the reliance on the Thunderbolt TM and needing Master Ball to be obtained quickly.

 

[DrumstickGaming]

B-Tier:
The following Pokemon claim a lot of OHKOs or 2HKOs, but may experience difficulties contributing efficiently to major fights, mainly due to requiring item assistance or coming fairly late.

B-Tier

Bulbasaur

Availability: Early-game (Pallet Town, starter (RB); Cerulean City, from Melanie if Pikachu has a friendship of 147 or higher (Y)).
Typing: Valuable for Brock (RB), Misty, and Lorelei, while also being good for Giovanni and resisting Lt. Surge's STAB moves. However, outside of those, the typing tends to be bad offensively.
Stats: Bulbasaur has well-rounded stats with a focus on Special. Venusaur's base 80 Speed also allows it to always land critical hits when using Razor Leaf.
Movepool: Vine Whip eventually upgrades into Razor Leaf at level 30, with Body Slam or Double Edge via TM being strongly recommended for Bulbasaur to have a way to deal with Grass resistant foes. Swords Dance via TM at Silph Co has some marginal use in helping Bulbasaur sweep with Body Slam.
Major Battles: Bulbasaur is good during early-game Gyms, but its usefulness fades afterward, with only Giovanni, Lorelei, and Bruno being favorable matchups later on, though it can also muscle through Erika.
Additional Comments: Bulbasaur is very useful for key opponents, but, due to its shallow movepool, tends to struggle against many other opponents. Players of Yellow, due to a glitch, can use repeteadly potions on the starter Pikachu at full health to boost its friendship and thus obtain a Bulbasaur faster.

Bellsprout

Availability: Early-game (Route 24, levels 12-14) (BY)
Typing: Bellsprout's Grass / Poison typing is useful against Misty, Lorelei, and Giovanni, while resisting Lt. Surge, although it's not helpful against Koga and Agatha.
Stats: Bellsprout has good attacking stats and average defenses. Victreebel's 70 base speed allows it to always land criticals with Razor Leaf. Movepool: Vine Whip upgrades to Mega Drain through TMs and then to Razor Leaf at level 38, with Acid at level 29 acting as Poison STAB. Natural Growth helps it sweep with Vine Whip and Mega Drain, while Swords Dance via TMs can be combined with Acid or Body Slam / Double-Edge through TMs. Sleep Powder at level 18 allows Victreebel to set up or attack safely.
Major Battles: Bellsprout is excellent against Misty, Lt. Surge, Giovanni, Lorelei, and Bruno. It can also sweep other battles with Sleep Powder and Swords Dance. Agatha is a notoriously bad matchup, however.
Additional Comments: It is recommended to hold on evolving with a Leaf Stone from Celadon City until Lv38 to learn Razor Leaf. Victreebel performs great against some of the more difficult opponents like Lorelei and Misty and is useful elsewhere due to Sleep Powder.

Charmander

Availability: Early-game (Pallet Town, starter (RB); Route 24, from Damian (Y)).
Typing: Doesn't really provide it with any inherent advantages, other than Erika and Yellow Koga. Furthermore, it makes Misty and Lorelei harder and Fire is also resisted by Brock and Lance.
Stats: Well-rounded stats with good Speed and decent offenses.
Movepool: Ember is the only option until Mega Punch and Dig, which help get the line by until Slash at level 33. Flamethrower at level 46 and Swords Dance via TM are good options, with the latter combining well with Dig or Earthquake.
Major Battles: Charmander has a shaky performance before evolving into Charizard; it has to play around Onix's Bide against Brock, needs Dig to beat Lt. Surge, and has an average performance against Erika. Once it evolves into Charizard, it maintains neutral matchups against everyone but Lorelei.
Additional Comments: Charmander's problems stem from an underwhelming natural movepool until Slash and largely negligible major battle matchups. However, it performs significantly better from Slash onward.

Eevee (Jolteon)

Availability: Mid-game (Celadon Mansion top floor as a level 25 Eevee).
Typing: Pure Electric type makes it good for Lorelei while being weak to Giovanni's Ground types and resisted by Erika.
Stats: Jolteon has excellent Special and Speed with a 25.39% chance to score a critical hit, but it is frail physically.
Movepool: Jolteon must be taught Thunderbolt via TM to do anything of note: its movepool is very barren outside of Reflect via TM. Double Kick and Pin Missile can provide situational uses, with the former being helpful against Rock / Ground types and the latter being helpful against Grass and Psychic types respectively.
Major Battles: Erika, Giovanni, and Agatha give Jolteon problems, but it has no issues using Thunderbolt against most other foes, particularly against Lorelei. Pin Missile can provide situational use against Sabrina if you are at level 48 in Red and Blue (you learn it at level 36 in Yellow).
Additional Comments: A Thunderstone to evolve Eevee can immediately be obtained from the Celadon Dept. Store. Jolteon must be taught Thunderbolt via TM to be useful, but it perfoms rather well if you do so.

Geodude

Availability: Early-game (Mt. Moon).
Typing: Rock / Ground gives the Geodude line a bad matchup against Misty, Erika, and Lorelei, but a type advantage against Lt. Surge, Koga, Blaine, and Agatha.
Stats: Graveler and Golem are excellent physical tanks, but their Special and Speed are lacking.
Movepool: Geodude gets STAB via Rock Throw at level 16, picking up Selfdestruct at level 21 (and Explosion later on at level 43). It requires the Dig TM for Ground STAB to get it by until Earthquake at level 36 and mitigate Rock Throw's terrible accuracy. The Rock Slide TM midgame provides a great upgrade to Rock Throw.
Major Battles: Graveler and Golem lose to Misty, Erika, and Lorelei, but are great for Lt. Surge and Koga with Dig (except in Yellow, where Koga has the Venonat line) as well as Blaine and Giovanni (save for Viridian Gym in Yellow, where he has Earthquake). Golem has an advantage against Agatha and some of Lance, but it is weak to Bruno's Fighting moves.
Additional Comments: While Graveler and Golem have some reliability issues until the midgame, they are still solid choices for a playthrough in spite of their weaknesses and slight TM reliance for STABs.

Hitmonlee

Availability: Mid-game (Fighting Dojo in Saffron City, Level 30).
Typing: Fighting type allows Hitmonlee to be useful against Lorelei, but is questionable against Sabrina and is not particularly useful for Koga and Agatha.
Stats: Good Attack and Speed allow Hitmonlee to be a good physical sweeper, but any special attack will deal massive damage to it.
Movepool: Starts off with Meditate and Double Kick, learning Jump Kick at level 38. High Jump Kick at level 48 has a higher 85 power, but with 90% accuracy to compensate. Strength via HM can provide Normal coverage, with Body Slam and Double-Edge through TMs being alternatives.
Major Battles: Hitmonlee is useful against Giovanni, Lorelei, and Bruno and has an even matchup against Blaine. It can be useful for Sabrina if the AI doesn't use offensive moves. It typically struggles against the rest due to them resisting Fighting.
Additional Comments: While Hitmonlee is fairly good, a lot of opponents resist or are immune to its moves. It's a reasonably good Pokemon if you can account for this flaw. Crash damage from Jump Kick and High Jump Kick only does 1 damage in Red, Blue and Yellow, so it's not an issue.

Jigglypuff

Availability: Early-game (Route 3 (RB) or Route 5 (Y), level 3, 5, or 7)
Typing: Outside of Agatha and Bruno's Fighting-types, Normal gives Wigglytuff a neutral matchup against every major opponent.
Stats: Wigglytuff has incredibly high HP. Its Attack is good for the earlier portions of the game, but falls off later on. Its low Special means that it can only hit hard when it hits super effectively.
Movepool: Outside of Sing, its movepool is entirely TM-based. It should be taught Mega Punch (which later upgrades to Body Slam or Strength) and Seismic Toss to handle bulkier opponents. Other TMs include Ice Beam, Blizzard, Thunderbolt, Psychic, Water Gun, and BubbleBeam.
Major Battles: Wigglytuff handles Misty, Lt. Surge, and most of the Elite Four with Seismic Toss and potentially Sing, with Normal STAB dealing with Sabrina and TMs handling the other opponents. As the game goes on, it will need to put more opponents to sleep to compensate for its low stats.
Additional Comments: While most of its stats are not very high, Wigglytuff can still perform well against most fights thanks to high HP, Sing, and wide TM learnset. It is also in the Fast experience group, so it is easy to train and can outlevel opponents to compensate for its low stats. Jigglypuff should be evolved as soon as possible with Moon Stone due to not learning anything useful by level.

Machamp (Y)

Availability: Mid-game (trade a Cubone for Machoke in the Underground Path between Route 5 and Route 6).
Typing: Fighting allows the line to be useful against Lorelei, but is terrible against Sabrina and is not particularly useful for Koga.
Stats: Machamp has a very high Attack, although its other stats are not particularly notable. Its Speed stat gives its Karate Chop around 78% chance to land a critical hit.
Movepool: Machamp's only STAB moves are Low Kick (which it starts with) and Submission through TMs, with the former being preferred. Machamp greatly appreciates Rock Slide and Dig or Earthquake through TM. Karate Chop is useful for beating route trainers without wasting other moves' PP, but isn't useful for most major fights.
Major Battles: With Rock Slide and a Ground TM, the line performs well against Koga, Blaine, and Agatha, while Fighting STAB lets it handle Lorelei and most of Giovanni's Pokémon.
Additional Comments: Machamp's biggest flaw is the reliance on TMs to perform greatly, but is otherwise a strong Pokémon that can be trained easily due to traded experience. You can also catch a Machop in Rock Tunnel for a slightly earlier arrival, but it doesn't provide any notable advantages over the traded one. Note that you receive it as a Machoke from the trade, which then proceeds to evolve.

Magikarp

Availability: Early-game (Route 3 Pokemon Center from Magikarp salesman for $500).
Typing: Gyarados's Water / Flying typing leaves it weak to Lt. Surge but neutral to virtually everything else aside from Blaine and Giovanni which it has an advantage against.
Stats: Great stats all-around as Gyarados, with 125 base Attack and 100 Special standing out. Gyarados's other stats are slightly above average.
Movepool: Gyarados gets Bite at level 20 and Dragon Rage at 25. Combined with BubbleBeam via TMs, Gyarados beasts through the early-game and mid-game. Surf through HM and Ice Beam and Thunderbolt via TMs really help bolster Gyarados's performance, but the latter two aren't necessarily required. with Hydro Pump (level 41) and Hyper Beam (level 52) being alternatives.
Major Battles: Gyarados beasts through Misty with Bite and high Special and can take out Lt. Surge's non-Raichu Pokemon with BubbleBeam. Good for Erika with Dragon Rage or Ice Beam and great for Blaine and Giovanni with Surf. It is generally neutral against the Pokemon League, but can overpower Bruno with Surf and take on Lance with Ice Beam.
Additional Comments: Magikarp being virtually useless until Gyarados holds it back from being one of the best options in-game, as does its Slow growth rate.

Magnemite (Y)

Availability: Mid-game (Route 10, level 16, 18, 20, or 22).
Typing: Electric makes Magneton useful for Lorelei and some of Lance's Pokémon, but makes it useless against Giovanni and not very helpful against Erika.
Stats: Magneton has one of the highest Special stats in the whole game. While its other stats are not as high, 95 Defense allows Magneton to be somewhat bulky.
Movepool: Magneton is viable only when taught Thunderbolt through TMs. Outside of that, it doesn't possess any great offensive moves, so it can either be taught support moves like Thunder Wave, Toxic, and Reflect through TMs or moves with situational use, such as Double-Edge and Thunder through TMs.
Major Battles: Magneton performs very well against Lorelei and reasonably well against any other opponent that does not resist Electric, though Pokémon with high Special such as Gengar and Alakazam tend to avoid 2HKOs from it.
Additional Comments: Magneton is a strong Pokémon that can beat most neutral targets easily. Its biggest flaw is its shallow movepool, making it useless against any Pokémon that resists Electric.

Mankey (Y)

Availability: Early-game (Route 22, level 3 or 5).
Typing: Fighting lets Mankey be useful against Brock and Lorelei, but is terrible against Sabrina and is not particularly useful for Koga.
Stats: Primeape is fast and has a high Attack, though it's not very bulky. Both Mankey and Primeape are fast enough to always land critical hits with Karate Chop.
Movepool: Scratch upgrades to Karate Chop at level 15. Primeape's best Fighting STAB is Low Kick at level 9. It performs best with Dig through TMs and also appreciates the Rock Slide and Seismic Toss TMs.
Major Battles: Mankey is one of the only Pokémon that can quickly beat Brock in Yellow. In addition, it beats Lt. Surge just with Karate Chop and is good against Lorelei thanks to Low Kick, while Dig lets it handle Blaine and Agatha and Rock Slide helps against Koga.
Additional Comments: Mankey is a useful Pokémon in some very key matchups. However, it needs the Dig TM to achieve its best performance, although it's a solid team member if it gets access to it.

Pikachu (RB)

Availability: Early-game (Viridian Forest, level 3 or 5).
Typing: Electric is useful for Misty and Lorelei, though rather useless against Brock, Erika, and Giovanni.
Stats: Raichu is very fast, having a 19.58% chance of landing a critical hit. Its Attack and Special are also good, though Raichu is frail physically.
Movepool: Thundershock upgrades to Thunderbolt through TMs. Pikachu also learns Thunder Wave at level 9. Its coverage is rather poor, with the only viable alternatives being Seismic Toss and Body Slam or Double-Edge through TMs.
Major Battles: Pikachu is useful against Misty's Starmie (despite not beating it) by paralyzing it and then weakening it with Thundershock. It can also beat Lt. Surge's Raichu with a combination of Thunder Wave and Seismic Toss. After it learns Thunderbolt via TM, it performs well against most opponents that don't resist Electric, with Thunder Wave helping against Special walls like Alakazam and Gengar.
Additional Comments: Raichu is a handy Pokémon that can contribute in many fights by defeating opponents with Thunderbolt or spreading paralysis. However, Electric tends to be resisted quite often and Raichu doesn't possess the means to get past resistant opponents efficiently. Evolve with Thunderstone immediately, as Pikachu does not learn any useful moves by level at that point.

Seel

Availability: Late-game (trade a Ponyta (RB) or Growlithe (Y) in Cinnabar Island's Pokémon Lab).
Typing: Water makes the line useful against Blaine and Giovanni, while Ice gives it a valuable advantage against Lance. However, Water / Ice is not particularly useful against Lorelei.
Stats: Dewgong's stats are good, for most parts, though none of them are particularly high, with the highest being its 95 Special, though it can easily outlevel opponents with traded experience to compensate for that.
Movepool: Dewgong mainly uses Surf and Ice Beam or Blizzard through TMs. Strength is its best option against special attackers. Its fourth move can be a secondary STAB, such as Aurora Beam at level 35 or BubbleBeam through TMs, in order to not waste the stronger moves' PP.
Major Battles: Dewgong easily beats Blaine, Giovanni, and Bruno, while STAB Ice Beam or Blizzard handle Lance with little issue. It can also perform reasonably well against Sabrina with Strength.
Additional Comments: While Seel comes rather late, it makes up for that with its traded experience and Water / Ice typing, which gives it an easy matchup against Lance. Players of Yellow will receive it directly as a Dewgong (instead of a Seel) upon performing the in-game trade.


Snorlax

Availability: Mid-game (Routes 12 and 16, level 30, must use Poke Flute to wake up).
Typing: Outside of Agatha and Bruno's Fighting-types, Normal gives Snorlax a neutral matchup against every major opponent.
Stats: Massive HP and great Attack let Snorlax serve as a good tank, though its twin defenses are average and its Speed is among Kanto's slowest.
Movepool: Starts with Amnesia, Rest, and Headbutt, picking up Body Slam at level 35 for reliable STAB with paralysis potential (useful with how slow Snorlax is). Notably, Snorlax gets Double-Edge at level 48 (and Hyper Beam later) naturally or through TMs. Snorlax can make some use out of several special moves and Earthquake though TMs, especially when the former is combined with the use of Amnesia.
Major Battles: Snorlax generally performs well in major battles, 2HKOing most threats with Body Slam. Even Bruno only has Hitmonlee and Machamp with a few Fighting moves that they might not even use. Earthquake makes Snorlax good for Agatha if taught, and Amnesia + Ice moves work well against Lance (notably, Snorlax is only 3HKOed by Hyper Beam unless it is used by Dragonite, who 2HKOs with it).
Additional Comments: Snorlax is a great Normal-type, but its sluggish Speed and vulnerability to secondary effects inhibits it to generally picking off a few threats in major battles rather than outright sweeping teams. Rest + Poke Flute (or items) can remedy this, but they make battles take even longer, exacerbating the Speed issue.

Spearow

Availability: Early-game (Route 22, level 3 or 5 (RB) or level 2, 4, or 6 (Y)).
Typing: Flying is useful against Erika, Yellow Koga, and Bruno's Fighting-types, with Normal giving it a neutral matchup almost everywhere else. However, the typing is bad against Brock, Lt. Surge, and Lorelei.
Stats: Fearow is rather fast, having a 19.53% chance of landing a critical hit. Its Attack is also rather good, though Fearow is not very bulky. Movepool: Spearow starts off with Peck, which upgrades to Drill Peck at level 34 as Fearow. Its Normal STAB is Fury Attack at level 15 and later Double-Edge through TMs. As Fearow lacks coverage, its other moves could be support ones like Leer and Growl or Fly through HMs for fast travel.
Major Battles: Fearow performs well against Erika, Koga, Bruno's Fighting-types, and Agatha with Flying STAB. Normal STAB lets it handle Sabrina easily. Against the rest, it can either easily KO frail threats or support teammates with Growl and Leer.
Additional Comments: Spearow comes early and is useful in many matchups. However, it is virtually useless against Rock-type Pokémon and struggles against bulkier physical threats, unless it's hitting them super effectively.

Squirtle (Y)

Availability: Mid-game (from Officer Jenny in Vermillion City after beating Lt. Surge, level 10).
Typing: Water typing gives Squirtle an edge against Blaine, and Giovanni, while giving it a weakness to Erika.
Stats: Squirtle has good well-rounded stats with an emphasis on Defense.
Movepool: Squirtle starts with Water Gun or Bubble Beam through TMs, both of which upgrade to Surf later on via HM. Coverage options in the form of Mega Punch, Dig, and Ice Beam / Blizzard exist, but only an Ice move is really necessary. Strength serves as a more accurate Mega Punch replacement.
Major Battles: Squirtle performs well against Blaine, Giovanni, and Bruno. It is also useful against Lance with Ice Beam or Blizzard (though it may require healing) and for Koga as long as it avoids Sleep Powder. It generally struggles in other matchups, though it can take out some Pokémon if it has the appropriate move.
Additional Comments: Squirtle's biggest issues are that it doesn't come very early and that it comes very underleveled, so it has to be grinded to become useful. Outside of that, it is useful in a number of matchups and also provides useful HM utility.

Staryu

Availability: Mid-game (Route 19, level 15 (RB) or level 20 (Y)) (Super Rod).
Typing: Water gives it a type advantage against Blaine and Giovanni, while Psychic makes it useful against Koga, Bruno, and Agatha.
Stats: Starmie's high 115 Speed (which gives it a 22.46% of landing a critical hit) combines well with its good 100 Special. Its only particularly low stat is 60 HP.
Movepool: Starmie's movepool is entirely TM-based with options like Surf, Psychic, Thunderbolt, Ice Beam, and Blizzard. The more TMs it has access to, the more good matchups it will have.
Major Battles: Starmie can handle virtually every single opponent that it can face if it has the correct TMs; Thunderbolt handles Lorelei, Ice TMs handle Lance, and Surf and Psychic handle the rest. Sabrina is the only major opponent that is not weak to any of Starmie's moves.
Additional Comments: Staryu is a notable Water-type due to its large TM learnset. However, the earlier Staryu comes underleveled and is a hassle to grind. You can also catch Staryu at Seafoam Islands at a higher level (level varies per game, floor, and method of encounter), though it misses on the Koga matchup and will still be at a lower level than your team in most cases. Evolve with Water Stone immediately.

 

[DrumstickGaming]

C-Tier:
The following Pokemon are not great, but have a couple of positive traits that prevents them from being outright bad. These Pokemon will take some time to beat opponents due to failing to OHKO or 2HKO them.

C-Tier

Eevee (Flareon)

Availability: Mid-game (Celadon Mansion top floor as a level 25 Eevee).
Typing: Fire isn't really useful anywhere outside of Yellow Koga, but doesn't grant Flareon with outright bad matchups either outside of Lance.
Stats: Flareon's offensive stats are very high, with Flareon possessing one of the highest Attack stats in the whole game. However, it is not very fast or physically bulky.
Movepool: Flareon's movepool is rather poor, as it doesn't get many useful moves to take advantage of either of its offensive stats. Its physical options include Body Slam and Double-Edge through TMs, while special options include Fire Spin at level 36 (Y) or 44 (RB), Flamethrower at level 54 (RB) or 52 (Y), and Fire Blast through TMs.
Major Battles: Flareon is particularly good at KOing frail targets with a physical move, with bulkier threats being put in KO range with Fire Spin. Its Flamethrower and Fire Blast can also pick off KOs at the Pokémon League."
Additional Comments: Flareon has incredible offensive stats that are counterbalanced by a poor movepool and low Speed. Evolve with a Fire Stone immediately, as Eevee doesn't learn anything useful by level.

Exeggcute

Availability: Mid-game (Safari Zone, levels 23-27 (RB), 22-26 (Y))
Typing: Psychic is useful against Poison and unresisted by everyone except other Psychics. Grass is good against Giovanni and Lorelei.
Stats: Exeggutor has excellent Special and well-rounded stats everywhere else except Speed.
Movepool: Exeggcute joins with Hypnosis and Reflect and can learn Leech Seed at Lv28 which can be combined with the Toxic TM. Exeggutor doesn't learn much leveling up, but it's compatible with the Strength HM, the Psychic TM, and the Mega Drain TM.
Major Battles: Exeggutor defeats Koga, Bruno, and Agatha easily with Psychic and can hit Sabrina with Strength. Exeggutor can also target Lorelei with the Mega Drain TM.
Additional Comments: Evolve Exeggcute with Leaf Stone at level 28 after learning Leech Seed. Exeggutor's optimal performance relies on the Psychic TM. Without it, it struggles to defeat enemies efficiently, but it can still cheese through battles with Hypnosis or Toxic + Leech Seed. The Slow leveling rate worsens the amount of time that Exeggcute needs to catch-up.

Farfetch'd (RB)

Availability: Early-game (trade a Spearow in a house in Vermillion City).
Typing: Normal / Flying gives it a good matchup against Erika and Bruno's Fighting-types, but worsens the matchup against Lt. Surge and Lorelei.
Stats: Farfetch'd stats are rather low and do not hold it for long, though traded experience can help it outlevel opponents to compensate for that. Its Speed stat gives its Slash around 93% chance to land a critical hit.
Movepool: Farfetch'd greatly appreciates the Body Slam TM in order to hit hard immediately, with Fury Attack at level 15, Double-Edge through TMs, and Slash at level 39 being other alternatives. Swords Dance and Agility at levels 23 and 31 help it sweep, with the former combining well with all STAB moves bar Slash. Farfetch'd can also make a good HM slave, as it learns both Cut and Fly.
Major Battles: Farfetch'd generally needs to set up with Swords Dance and potentially Agility in order to sweep any team. This is unreliable at the Pokémon League, as its low bulk makes it hard to set up consistently. Farfetch'd can also just pick off frail targets with Slash critical hits.
Additional Comments: Farfetch'd can make a great HM slave and also is easy to train due to traded experience. However, due to its low stats, it is forced to rely on setup against every major opponent and falls off at the Pokémon League anyways.

Goldeen

Availability: Mid-game (Fuchsia City, level 23 (RB); Route 24, level 30 (Y)) (Super Rod).
Typing: Water provides it with a good matchup against Blaine and Giovanni, but isn't too useful elsewhere.
Stats: Seaking's stats are all around okay, but not particularly high. It can run mixed sets with reasonable effectiveness.
Movepool: Seaking mostly uses Surf and Ice Beam or Blizzard through TMs, though it can be given the Double-Edge TM for physical coverage. Waterfall at level 39 can act as a secondary STAB move to Surf to preserve PP.
Major Battles: Outside of Blaine and Giovanni, Seaking also handles Bruno easily. With Double-Edge, it also has a good matchup against Sabrina, while an Ice-type move helps against Lance.
Additional Comments: Goldeen can contribute to some matchups thanks to its Water typing and ability to run mixed sets, though it generally doesn't stand out from the other Water-types in the game.

Growlithe (R)

Availability: Mid-game (Route 7, level 18 or 20).
Typing: Fire, outside of giving it a good matchup for Erika, is pretty neutral almost everywhere else outside of Lance, who Arcanine is bad against.
Stats: Arcanine's stats are all around good, most notably having a high Attack and being relatively fast.
Movepool: The line relies entirely on Ember and TMs, as the only useful level-up move Growlithe learns, Flamethrower, comes at level 50. Arcanine's best options from TMs are Body Slam, Double-Edge, Dig, and Fire Blast.
Major Battles: Arcanine performs the best if it knows Dig, as it can beat Koga, Blaine, and Agatha with it. It also performs well against Sabrina and its Fire Blast can easily pick off KOs at the Pokémon League.
Additional Comments: Growlithe's best performance is very reliant on the Dig TM and its viability drops significantly if it doesn't get it. Evolve with Fire Stone immediately, as waiting for Flamethrower at level 50 is not worth it.

Horsea

Availability: Mid-game (Route 19, level 15 (RB); Route 12, level 20 or 25 (Y)) (Super Rod).
Typing: Water gives it an advantage against Bruno and Giovanni and neutral matchups elsewhere, bar Erika and Lorelei.
Stats: Seadra's stats are mostly good, as it's able to outspeed many opponents and hit them rather hard, though its HP is low.
Movepool: Seadra's movepool isn't huge, consisting of Surf and Ice Beam or Blizzard through TMs and Hydro Pump at level 52. It can use Smokescreen to cripple more difficult opponents.
Major Battles: Beats Blaine, Giovanni, and Bruno with Surf, while Lance can be handled with an Ice TM. Erika can also be weakened with Ice Beam, though the line isn't doing much there anyways.
Additional Comments: Horsea contributes mainly with its Water typing and good stats, though it's rather useless in many matchups. Players of Red and Blue can catch it directly as Seadra on Route 23 after obtaining the Rainbow Badge, with players of Red also being able to catch it at a higher level at Seafoam Islands with the help of Repels. Players of Yellow can also reel in a Seadra at level 25 or 35, though at a 30% encounter rate.

Kabuto

Availability: Late-game (revive Dome Fossil at Cinnabar Island's Pokémon Lab, level 30).
Typing: Water is useful for Blaine and Giovanni and is neutral everywhere else, except against Lorelei. Rock is useless, as the line does not learn any Rock-type moves.
Stats: Kabutops has a high Attack and is relatively fast, allowing it to always land critical hits with Slash. However, its 70 Special is not really high, so it will struggle to hit hard with Water moves.
Movepool: Kabutops's best STAB move is Surf and can be combined with Ice Beam or Blizzard through TMs. It can also sweep teams with Swords Dance and Double-Edge through TMs. Slash at level 39 allows the line to beat Route trainers rather quickly.
Major Battles: Kabutops performs well against Blaine, Giovanni, and Bruno, with Swords Dance and Double-Edge allowing it to sweep the others except Agatha. It can also be useful against Lance with an Ice TM.
Additional Comments: Kabuto comes rather late, though it can take on more opponents than most Water-types if it takes the time to set up Swords Dance, though it will have to heal often if using Double-Edge.

Kangaskhan

Availability: Mid-game (Safari Zone (Central Area (east), level 25 (RB); Area 2, level 28 or 33 (Y)).
Typing: Normal typing gives Kangaskhan neutral matchups everywhere bar Agatha's Ghost-types and Bruno's Fighting-types.
Stats: Kangaskhan has a relatively good Attack and Speed, coupled with good Defense and HP. However, its Special is low.
Movepool: Kangaskhan's best STAB move is Strength through HMs. Useful TMs include Earthquake, Rock Slide, Seismic Toss, and Surf to handle Rock / Ground Pokémon. It also learns other special TMs like Ice Beam, Blizzard, Thunderbolt, and Fire Blast, though all have only situational uses due to Kangaskhan's lacking Special.
Major Battles: Up until the Elite Four, Kangaskhan is able to reasonably OHKO or 2HKO most opponents that take neutral damage from its STABs, with physical coverage improving matchups when it hits super effectively. At the Pokémon League, it will generally OHKO or 2HKO Pokémon with super effective Rock Slide or Earthquake.
Additional Comments: Kangaskhan is a strong Pokémon that can learn many useful moves, but is hard to both find and catch. However, in Yellow, its encounter rate in Area 2 is slightly higher, being 15%.

Krabby

Availability: Mid-game (Vermillion City, level 15 (RB); Route 10, level 25, caught as Kingler (Y)) (Super Rod).
Typing: Water makes Krabby useful against Blaine and Giovanni, but is not good against Erika, Lorelei, and Lance.
Stats: Kingler has one of the highest Attack stats in the entire game, although its low Special prevents it from using STAB moves effectively. Its HP is also very low, though its Defense is high. Its base 75 Speed guarantees critical hits on its Crabhammer.
Movepool: The line's most notable move is Crabhammer at level 42, which is the only STAB move that Kingler can hit hard with. It can also sweep with Swords Dance and Strength through TMs. Surf and Ice Beam or Blizzard can be taught via TMs, though Kingler doesn't use them well.
Major Battles: Kingler is good for Blaine, Giovanni, and Bruno just with Crabhammer. Sabrina can be handled with Strength as long as you are not outsped or hit constantly. The other matchups bar Agatha can be swept with Swords Dance and Strength.
Additional Comments: Due to its low Special, Kingler cannot put most of its moves to great use, so it has to rely on setup to perform well against major opponents that are not weak to Water. Players of Blue and Yellow can also catch Krabby or Kingler at a higher level at Seafoam Islands, but it might still need grinding. Players of Red and Blue can also fish for Kingler on Route 23 after obtaining the Rainbow Badge.

Lapras

Availability: Mid-game (from an NPC on Silph Co.'s 7th floor, after defeating rival, level 15).
Typing: Water makes it useful for Blaine and Giovanni, while Ice makes it good for Lance. The typing is not very useful against Lorelei.
Stats: Lapras is very bulky due to its 135 HP and also has relatively good Special. However, it is not very fast, so it will be outsped sometimes. Movepool: Lapras uses Surf from HM and Ice Beam at level 38. Sing at level 16 allows it to beat opponents it wouldn't be able to beat otherwise. Lapras can also be taught Thunderbolt and Psychic through TMs, with the former improving the matchup against Lorelei. Body Slam at level 25 provides physical coverage.
Major Battles: Lapras handles Blaine, Giovanni, Bruno, and Lance with just STAB moves. Sabrina can also be handled to some extent with Body Slam, while Lorelei is a good matchup with Thunderbolt.
Additional Comments: Lapras is a strong Pokémon with a good movepool, but it comes very underleveled and is a hassle to train due to its slow growth rate. Furthermore, you need to ensure you have enough route trainers so Lapras can be trained efficiently, so you may have to fight your rival at Silph Co. as soon as possible to obtain Lapras.

Machop (RB)

Availability: Mid-game (Rock Tunnel, level 15 or 17).
Typing: Fighting allows the line to be useful against Lorelei, but is terrible against Sabrina and is not particularly useful for Koga.
Stats: The line's only notable stat is their Attack, which is particularly high for Machoke and excellent as Machamp. Machoke and Machamp's Speed give their Karate Chop around 70% and 78% chance to land a critical hit respectively.
Movepool: The line's only STAB moves are Low Kick at level 20 and Submission through TMs, with the former being preferred. The line greatly appreciates Rock Slide, Dig, or Earthquake through TM. Karate Chop is useful for beating route trainers without wasting other moves' PP, but isn't useful for most major fights.
Major Battles: With Rock Slide and a Ground TM, the line performs well against Koga, Blaine, and Agatha, while Fighting STAB lets it handle Lorelei and most of Giovanni's Pokémon. It can also beat Lance's Dragon-types, as they will always use Agility or Barrier against it.
Additional Comments: Machop comes rather underleveled and weak, so it takes some effort to evolve it. Furthermore, its evolutions perform strongly only when taught the correct TMs. Both Machoke and Machamp have a similar performance, so even if you cannot trade to evolve, you won't generally miss out on too much.

Magnemite (RB)

Availability: Late-game (Power Plant, level 21 or 23).
Typing: Electric makes Magneton useful for Lorelei and some of Lance's Pokémon, but makes it useless against Giovanni.
Stats: Magneton has one of the highest Special stats in the whole game. While its other stats are not as high, 95 Defense allows Magneton to be somewhat bulky.
Movepool: Magneton is viable only when taught Thunderbolt through TMs. Outside of that, it doesn't possess any great offensive moves, so it can either be taught support moves like Thunder Wave, Toxic, and Reflect through TMs or moves with situational use, such as Double-Edge and Thunder through TMs.
Major Battles: Magneton performs very well against Lorelei and reasonably well against any other opponent that does not resist Electric, though Pokémon with high Special such as Gengar and Alakazam tend to avoid 2HKOs from it.
Additional Comments: Magneton can beat many neutral opponents easily with its high Special and Thunderbolt, but it comes rather late and has a shallow movepool. You can also catch it as Magneton at level 32 or 35, though it's at 10% encounter rate, so Repel tricking is needed to find it fast.

Mankey (R)

Availability: Early-game (Route 5, level 10, 12, 14, or 16).
Typing: Fighting lets Mankey be useful against Lorelei, but is terrible against Sabrina and is not particularly useful for Koga.
Stats: Primeape is fast and has a high Attack, though it's not very bulky. Both Mankey and Primeape are fast enough to always land critical hits with Karate Chop.
Movepool: Scratch upgrades to Karate Chop at level 15. Primeape's only Fighting STAB is Submission through TMs. It performs best with Dig through TMs and also appreciates the Rock Slide and Seismic Toss TMs.
Major Battles: If taught Dig, the line performs well against Lt. Surge, Koga, Blaine, and Agatha, with Rock Slide or Submission helping against Lorelei. Blaine can also be handled by Rock Slide.
Additional Comments: Mankey is reliant on the Dig TM to perform well against most fights. However, should it get access to that TM, it will have a good performance.

Meowth

Availability: Early-game (Route 5, levels 10, 12, 14, or 16) (B).
Typing: Normal is neutral against everything except against Agatha's Ghost-types, and also fears Fighting-type moves from Bruno.
Stats: Persian's high 115 Speed gives it a 22.46% chance of landing a critical hit and ensures that Slash will always result in one as well. The other stats are not particularly high and fall off at the Pokémon League.
Movepool: Its STAB moves are Bite at level 12, Body Slam or Double-Edge through TMs, and Slash at level 51. Pay Day at level 17 is a good way to earn extra money. Coverage includes Water Gun / Bubble Beam and Thunderbolt through TMs, though only a Water move is really needed.
Major Battles: Persian rarely achieves a reliable sweep and is instead better off outspeeding and KOing frailer threats like the Abra line, though it can perform well against Lorelei with Slash. It also performs well against Giovanni with Bubble Beam or Water Gun.
Additional Comments: Meowth's biggest contributions are its ability to generate extra money and the ability to outspeed and KO frail Pok&ecute;mon.

Oddish

Availability: Early-game (Route 24, levels 12-14) (RY)
Typing: Useful against Misty and Lorelei, as well as good for Giovanni and resisting Lt. Surge, although it's not helpful against Koga and Agatha.
Stats: Vileplume has well-rounded stats except for its lackluster 50 Speed.
Movepool: Absorb and Sleep Powder carry Oddish to Acid at level 24 and Mega Drain through TMs later on. Vileplume can learn the Swords Dance TM to sweep teams. The Body Slam and Double-Edge TMs are superior alternatives to Acid.
Major Battles: Oddish is excellent against Misty, Lt. Surge, Giovanni, Lorelei, and Bruno. It can also sweep other battles with Sleep Powder and Swords Dance. Agatha is a notoriously bad matchup, however.
Additional Comments: It is recommended to evolve Gloom immediately with a Leaf Stone, as it does not learn any useful moves by level at this point. Oddish is also stuck with Absorb for a long time, until it learns Acid. Oddish relies on Sleep Powder often, though Swords Dance helps its sweeping prowess.

Omanyte

Availability: Late-game (revive Helix Fossil at Pokémon Lab on Cinnabar Island, level 30).
Typing: Water typing gives it a type advantage against Blaine and Giovanni, but is resisted by Lorelei. Rock typing does not have offensive use, as the line does not learn any Rock-type moves.
Stats: Omastar has great Defense and Special. On the other hand, it is very slow.
Movepool: Omastar mostly uses Surf and Ice Beam / Blizzard through TMs. It doesn't learn anything else that's notable, outside of Hydro Pump at level 49 and support moves from TMs like Reflect and Toxic.
Major Battles: Omastar performs well against Blaine, Giovanni, and Bruno, with Ice Beam or Blizzard helping it against Lance. The other opponents tend to have Pokémon with high Special, allowing them to withstand Omastar's attacks.
Additional Comments: Omanyte is strong, but the late arrival and the abundance of specially bulky Pokémon in the late-game hold it back.

Poliwag

Availability: Mid-game (Celadon City, level 23 (RB); Route 23, level 30 or 40 (Y)) (Super Rod, reeled in as Poliwhirl).
Typing: Water makes Poliwrath useful against Blaine and Giovanni, while Fighting gives it a better matchup against Lorelei. The typing is not particularly good for Sabrina and Lance.
Stats: Most of Poliwrath's stats are okay, but its Special is not particularly high and thus will need Amnesia boosts to hit neutral targets harder. Movepool: Poliwrath mainly uses Surf and Ice Beam or Blizzard, with Submission through TMs being its only Fighting STAB. Poliwhirl learns Hypnosis at level 16 and Amnesia at level 41, which help it sweep opponents.
Major Battles: Poliwrath easily beats Blaine, Giovanni, and Bruno and can also contribute against Erika and Lance with Ice Beam. However, it will often need Amnesia boosts and sometimes Hypnosis in order to achieve a sweep.
Additional Comments: Poliwrath is very reliant on Amnesia boosts to perform well in most fights. In Yellow, you can fish on Route 23 after defeating Erika, though you could potentially fish for one at Route 22 for an earlier, but underleveled Poliwhirl. Also note that level 40 Poliwhirl are rather uncommon, so it may take you some time to find one. Evolve with Water Stone at level 41 after learning Amnesia.

Psyduck (RB)

Availability: Mid-game (Route 24, level 15) (Super Rod).
Typing: Water allows Psyduck to perform well against Blaine and Giovanni, but doesn't provide it with any advantages elsewhere.
Stats: Golduck's stats are good, but not very high. The highest one is its 95 Special.
Movepool: Golduck relies on Surf and Ice Beam or Blizzard through TMs. It can be taught Dig and Seismic Toss through TMs for coverage.
Major Battles: Golduck beats Blaine, Giovanni, and Bruno with no problems. With an Ice TM, it can handle Lance, as well as Erika with Ice Beam only. It can also potentially contribute against Agatha if it knows Dig.
Additional Comments: The line contributes mostly with Water typing and good stats, but is not particularly amazing. Furthermore, Psyduck is rather weak and comes underleveled. Golduck can also be caught at Seafoam Islands at a higher level, though that comes later.

Rattata

Availability: Early-game (Route 1, level 2-4).
Typing: Normal is useless against Brock and Agatha's Ghost-types and is weak to Bruno's Fighting moves, but is neutral elsewhere.
Stats: Rattata is a fast Pokémon having a 18.95% chance of landing a critical hit, with a relatively fine 81 Attack stat. However, its stats fall off towards the later portions of the games and its bad Special prevents it from putting a good use to the many special TMs it learns.
Movepool: Rattata's Tackle upgrades to Hyper Fang at level 14 and later Body Slam or Double-Edge through TMs. Super Fang at level 41 can be useful for weakening a difficult opponent. Raticate greatly appreciates Dig, as it gives it some good matchups in the late- and end-game, and also learns some special TMs like BubbleBeam, Water Gun, Thunderbolt, Ice Beam, and Thunderbolt.
Major Battles: Rattata performs well in the early-game, being able to contribute against Brock with Tail Whip and sweep Misty and Lt. Surge. After that, Raticate starts to drop in terms of viability and is generally limited to KOing frail threats unless it's taught Dig, which allows it to perform well against RB Koga, Blaine, and Agatha.
Additional Comments: While Raticate starts off strong, it eventually falls off due to its unimpressive stats and is reliant on the Dig TM to maintain viability throughout the game.

Rhyhorn

Availability: Mid-game (Safari Zone, Central Area (hub) at level 25 (RB) or Area 2 at level 25 (Y)).
Typing: Rock / Ground is useful for Koga, Blaine, and Agatha, while being outright bad only against Erika and Lorelei.
Stats: The line hits hard and is bulky physically, but is slow and is vulnerable to special attacks.
Movepool: The line greatly appreciates Rock Slide and Dig or Earthquake through TMs. It can also be taught Surf (as a Rhydon) and Strength for coverage and HM utility.
Major Battles: Other than Koga, Blaine, and Agatha, Rhydon is also useful against Giovanni, Bruno, and Sabrina, though it has to watch out for super effective moves from Giovanni and Bruno and is threatened by Sabrina's special attacks. It can also contribute against Lance, though his team in Yellow possesses more super effective moves that threaten Rhydon.
Additional Comments: Rhydon can contribute to many fights with its powerful attacks, but it levels up slowly and evolves late. In Yellow, you can also obtain a Rhydon from an in-game trade at Pokémon Lab in Cinnabar Island for a Golduck, though it skips the Koga matchup and you either have to grind a Psyduck or catch an underleveled Golduck.

Shellder

Availability: Mid-game (Vermillion City, level 15 (RB); Route 18, level 20, 30, or 40 (Y)) (Super Rod).
Typing: Water makes the line good against Blaine and Giovanni, while Ice gives it a type advantage against Lance. The typing is useless against Lorelei.
Stats: Cloyster has an okay Special and a really high Defense that is balanced out by low HP. 70 Speed lets it outspeed most opponents.
Movepool: The only notable level-up moves Shellder learns are Clamp at level 23, which can slowly weaken an opponent, and Aurora Beam at level 30. Outside of those, Cloyster learns Surf and Ice Beam or Blizzard (as well as Self-Destruct and Explosion) through TMs.
Major Battles: Beats Blaine, Giovanni, and Bruno easily with Water STAB, while Lance falls to Ice moves. With Clamp, Cloyster can slowly take out other opponents that can withstand special attacks easily.
Additional Comments: Shellder has a great typing, but levels up slowly and often comes underleveled, though players of Red and Blue can catch it later at Seafoam Islands at a higher level. While players of Yellow can get it at level 40, those are rather uncommon. Evolve with Water Stone either at level 23 after learning Clamp or at level 30 after learning Aurora Beam if you are not planning on teaching it an Ice TM.

Slowpoke (RB)

Availability: Mid-game (Route 23, level 23, caught as Slowbro) (Super Rod).
Typing: Water makes it useful against Blaine and Giovanni, while Psychic gives it a type advantage against Koga, Bruno, and Agatha.
Stats: Slowbro is a bulky Pokémon that is very slow and generally needs Amnesia boosts to hit hard with its 80 Special.
Movepool: Slowbro's offensive options are Surf, Psychic, and Ice Beam or Blizzard through TMs. Amnesia at level 44 allows it to sweep opponents that are not hit super effectively by its moves.
Major Battles: Slowbro handles Koga, Blaine, Giovanni, and Bruno with little trouble. With Psychic, it can also help against Agatha if it doesn't get crippled by status moves and can help against Lance with an Ice TM. Amnesia boosts allow it to contribute elsewhere.
Additional Comments: Slowpoke comes underleveled and is hard to train due to its slow growth rate. It is reliant on Amnesia boosts to OHKO a number of opponents and its low Speed lets it get worn out easily. Slowbro can also be caught at a higher level at Seafoam Islands via Repels.

Tauros

Availability: Mid-game (Safari Zone (Area 3, level 26 (RB); level 21 (Y)).
Typing: Normal typing gives Tauros neutral matchups everywhere bar Agatha's Ghost-types and Bruno's Fighting-types.
Stats: Great Attack and Defense combined with an incredible 110 Speed make Tauros a speedy physical tank with average HP and Special.
Movepool: Tauros starts with its only decent natural STAB in Stomp. TMs are where Tauros shines, with Body Slam or Strength being good STAB that can be complimented by Earthquake (the combination which hits everything neutrally). Thunderbolt and Ice Beam or Blizzard are also decent options due to Tauros's passable Special.
Major Battles: Tauros generally uses Body Slam to 2HKO things in major battles, being good for Sabrina as well as Blaine, Giovanni, and Agatha if you teach it Earthquake. It is neutral elsewhere save for Bruno unless you give it Thunderbolt for Lorelei and Ice Beam or Blizzard for Lance.
Additional Comments: Tauros is one of the best Normal types, but its sheer rarity combined with Safari Zone mechanics make it only a decent choice overall. Note that Tauros has a slightly higher 10% encounter rate in all Areas it is found in in Yellow (in RB, the highest is 4% in Area 3).

Tentacool

Availability: Mid-game (Viridian City (level 15) (RB); Vermillion City (Super Rod, 10, 15, or 20) (Y)).
Typing: Water / Poison makes Tentacruel good for Blaine and Giovanni, though it makes Tentacruel weak to Sabrina and awkward for Lorelei.
Stats: Great HP and Speed combined with a beefy 120 Special make Tentacruel a special sweeper with a critical hit rate of 19.53%, though its physical stats are low.
Movepool: Any level 15 Tentacool already have Wrap as well as Acid, and can be taught Surf via HM. Barrier at level 35 can bolster Tentacruel's Defense, while Hydro Pump can deal heavy, albeit inaccurate damage if desired. Mega Drain, Ice Beam, and Blizzard can be taught through TMs.
Major Battles: Tentacruel can be good for Erika with Ice Beam and Surf its way to victory against Koga, Blaine, Giovanni, and Bruno. Sabrina, Lorelei, and Agatha will be somewhat difficult due to their Special bulk, but Lance is easily handled with either Ice Beam or Blizzard.
Additional Comments: Tentacool is a great Water type, but it coming underleveled combined with the unfeasibility of getting a high leveled one knock its viability down. The Tentacool on Route 21 can come as high as level 40 in RB and 30 in Yellow, but are very rare even with Repel.

Voltorb (RB)

Availability: Mid-game (Route 10, level 14, 16, or 17).
Typing: Electric gives Voltorb a good matchup against Lorelei and a neutral matchup everywhere else bar Erika and Giovanni.
Stats: Electrode is the fastest Pokémon in the entire game and has a 27.34% chance of landing a critical hit. Its other stats are not as high, with its Special reaching 80.
Movepool: The line is heavily reliant on the Thunderbolt TM for its best performance. Outside of that, it doesn't have much to go with, other than Selfdestruct and Explosion at levels 27 (as Voltorb) and 50 (as Electrode), though it generally has to weaken the target first to KO it. Support moves like Thunder Wave and Toxic can be taught through TMs.
Major Battles: Electrode performs well against Lorelei and Bruno's Fighting-types and can KO Lance's Gyarados and Aerodactyl. Outside of that, it can generally beat neutral targets that are not too bulky specially, though it is virtually useless against anything that resists Electric.
Additional Comments: Voltorb's biggest contribution is its great matchup against Lorelei. Although its offensive stats are not high, they are compensated by its high chance of landing a critical hit, allowing it to maintain viability against bulkier targets. You can also obtain it directly as an Electrode at level 43 at the Power Plant by picking up one of the fake item balls at the cost of a later arrival.

Vulpix

Availability: Mid-game (Route 7, level 18 or 20 (B); buy at Rocket Game Corner for 1000 coins (Y)).
Typing: Outside of a type advantage against Erika and Yellow Koga, Fire typing doesn't give it good matchups, with Lance also resisting it.
Stats: Ninetales is fast, having a 19.53% chance of landing a critical hit. It also has a great Special, but its other stats are lacking.
Movepool: Vulpix has to struggle with Ember until it learns Flamethrower at level 35. It also learns Confuse Ray at level 28. As a Ninetales, it appreciates the Dig TM to improve some matchups, while Fire Blast through TMs is a stronger Fire STAB move.
Major Battles: It struggles as a Vulpix against anything, though its performance improves a lot once it learns Flamethrower and evolves. With Flamethrower, it can perform well against most opponents that do not resist it, with Dig giving it a better matchup against Blaine and Agatha. Additional Comments: While Ninetales ia good Pokémon, you have to put up with the bad Vulpix period in order to use it effectively. While you could evolve it with a Fire Stone immediately, Ninetales would have no reliable and powerful STAB move this way. You also have to spare the Dig TM for it so it can have some better matchups.

Weedle (RB)

Availability: Early-game (Viridian Forest, level 3-5 (R); level 3 (B)).
Typing: Bug / Poison makes it good for Misty, Erika, Koga, and Giovanni's Poison types. It's a double-edged sword against Sabrina (as both hit each other super effectively) and neutral elsewhere.
Stats: Beedrill's HP, Attack, and Speed are all roughly average, with its defenses and Special being poor.
Movepool: Beedrill struggles with Poison Sting and later Fury Attack until it learns its main STAB in Twineedle at level 20 (to which Pin Missile can serve as an alternative at level 32). Agility at level 35 or Swords Dance via TM help Beedrill sweep, with Double-Edge serving as Normal coverage.
Major Battles: Beedrill loses to Brock, but sweeps Misty and Erika easily while being okay for Lt. Surge. Beedrill is also good for Koga and Sabrina if it can setup, though it must be wary of Psychic moves from the latter. Beedrill loses to Blaine while being decent for Giovanni's Poison types, though it will generally struggle to setup at the Pokemon League due to lacking stats.
Additional Comments: Beedrill is the only Bug type with proper STAB and is actually quite good for roughly half the game after learning Twineedle thanks to the ubiquity of types weak to Bug. However, it's average ultimately due to its stats falling off and relying on setup to sweep later on. Weedle is much more common in Red than in Blue.

 

[DrumstickGaming]

D-Tier:
The following Pokemon have more negative traits than positive ones, although their positive traits allow them to be somewhat usable. These Pokemon are good only in specific matchups and are generally useless otherwise.

D-Tier:

Aerodactyl

Availability: Late-game (revive from Old Amber at Pok&eacute'mon Lab in Cinnabar Island, level 30).
Typing: Rock / Flying only provides it with a type advantage against Bruno's Fighting-types and a resistance to Blaine, but worsens the matchup against Lorelei. Rock is also useless offensively, as Aerodactyl learns no Rock-type moves.
Stats: Aerodactyl's Speed is incredibly high and grants it a 25.39% chance of landing a critical hit. Its 105 Attack is also relatively high, though Aerodactyl is not very bulky.
Movepool: Aerodactyl's STAB moves consist of Wing Attack and Fly and later Sky Attack through TMs. Its only other forms of coverage include Bite at level 38, Fire Blast and Double-Edge through TMs, and Hyper Beam at level 54.
Major Battles: Aerodactyl performs well against Sabrina and Blaine. At the Pokémon League, it can OHKO frailer Pokémon like Agatha's Ghost-types and Lance's Dragonair with Sky Attack. The other matchups tend to be bad for Aerodactyl due to its limited movepool and low bulk.
Additional Comments: Aerodactyl comes rather late and is not particularly useful in most of the remaining fights. Old Amber can be obtained in the backroom of the Pewter Museum of Science, though you need Cut to access the room.

Caterpie

Availability: Early-game (Virdian Forest, level 3 (R), 3-5 (B), or 3-6 (Y)).
Typing: Bug / Flying is only useful for resisting Erika. It gives Butterfree a weakness to RB Koga, Lt. Surge, and Blaine and is useless offensively, as Butterfree doesn't learn STAB moves at all.
Stats: Butterfree's stats are very high for the earlier portions of the game, though as the game goes on, they will start to fall off.
Movepool: Butterfree learns Confusion and Sleep Powder at levels 12 and 17 in RB and levels 10 and 15 in Yellow. Confusion upgrades to Psybeam at level 32 (RB) or 34 (Y) or to Psychic through TMs. Mega Drain through TMs provides coverage against Rock-types.
Major Battles: With a Psychic move, it can beat Brock, Koga, Erika, and Bruno with little difficulty. Brock is especially notable as in comparison to most other mons, Butterfree can hit hard with Confusion and play around Bide with Harden. Against the rest, it typically has to put them to sleep with Sleep Powder and take a lot of time KOing them with Psybeam / Psychic.
Additional Comments: Butterfree is good for few fights, but its low stats force it to put most opponents to sleep and slowly take them out, which generally takes a lot of time to pull off.

Chansey

Availability: Mid-game (Safari Zone, Center Area (hub), Center Area (east), Area 2)
Typing: Normal typing has neutral matchups everywhere save for Agatha and Bruno's Fighting types (which Chansey would use Psychic for).
Stats: 250 base HP and 105 Special make Chansey the ultimate Special tank, though its Speed is low and its physical stats are lacking.
Movepool: Chansey's natural learnset isn't really worth mentioning aside from Sing and Light Screen at levels 24 and 48. However, Chansey has an expansive TM movepool of great Special options like Ice Beam, Thunderbolt, and Psychic, with options like Reflect + Softboiled and Thunder Wave also available for utility if desired.
Major Battles: It is recommended to give Chansey Psychic and Ice Beam to succeed against Koga, Giovanni (watch out for physical moves though), Bruno, Agatha, and Lance. Thunderbolt can help for Lorelei as well.
Additional Comments: Chansey's 1% or 4% encounter rate, low catch rate, and high reliance on TMs prevent it from being tiered higher, though its Fast growth rate keeps it relevant. Chansey is not a bad Pokemon, but it simply requires too much investment needed to perform effectively.

Cubone

Availability: Mid-game (Poémon Tower, level 20 (all games) or 22 (RB)).
Typing: Ground is useful for RB Koga, Blaine, and Agatha, but bad for Erika and Lorelei.
Stats: Marowak's stats outside of 110 Defense are not particularly high; it is rather slow and its 80 Attack isn't that notable. Its low Special also prevents it from using the special TMs it can learn.
Movepool: Although Cubone starts with Bone Club, it vastly prefers Dig or Earthquake through TMs due to their higher power and accuracy. It also learns Bonemerang at level 48 as Marowak as a replacement, though it comes rather late. As it cannot use special TMs like BubbleBeam, Ice Beam, and Fire Blast due to its low Special, it is limited only to Strength for physical coverage.
Major Battles: Marowak is typically useful only against Ground-weak opponents like RB Koga, Blaine, and Agatha and generally struggles to OHKO the other opponents due to its unimpressive Attack.
Additional Comments: Despite learning Ground moves by level, they are either weak or come late, thus Cubone is still reliant on the Ground TMs to be useful. Furthermore, even with them, Cubone is generally limited in its contributions when it doesn't have a type advantage. In Yellow, Cubone is available from the fifth floor of Pokemon Tower onwards.

Dratini

Availability: Mid-game (buy at Rocket Game Corner for 2800 (R) or 4600 (B) coins; Safari Zone (Central Area (hub), with Super Rod) (Y)).
Typing: Dragon gives it a bad matchup against Lorelei, though it also resists Erika. It is useless offensively, since Dragon STAB moves do not exist.
Stats: Dragonair's stats are not particularly high, with Dratini's stats being even worse. Dragonite's stats are very high, but, due to late evolution, it is unlikely that the line will get to use them.
Movepool: It learns a variety of TMs, such as Surf, Body Slam, Ice Beam, Blizzard, Thunderbolt, and Fire Blast. It can also utilize the combination of Wrap and Thunder Wave or Agility to slowly weaken the opponent.
Major Battles: With Surf, Dratini proves useful for Blaine, Giovanni, and Bruno. Ice Beam can also improve the matchup against Erika and Lance. Thunder Wave + Wrap can be used to put opponents in range for one of its moves to KO them.
Additional Comments: Dratini is not easy to obtain and performs well only in few matchups, with contested TMs being needed to perform better in more. It also levels up slowly. In Yellow, you can reel in a level 15 Dragonair (10% encounter rate) in the Safari Zone's Central Area (hub).

Ekans (R)

Availability: Early-game (Route 4, level 6, 8, 10, or 12) (R).
Typing: Poison only gives it a resistances Erika and Koga and a weakness to Sabrina. Arbok doesn't learn any STAB moves, making its type useless.
Stats: Arbok's Attack and Speed are the only mildly impressive stats it has, though even they fall off later on. It is also fairly weak as Ekans. Movepool: Ekans relies on Leer, Wrap, and Poison Sting until it learns Bite at level 17. Arbok depends on the Dig or Earthquake TM (the former being preferred early on) to perform well. Other useful moves include Glare at level 27 and Mega Drain, Rock Slide, and Strength through TMs.
Major Battles: If it knows Dig (or Earthquake later on), it will perform well against Lt. Surge, Koga, Blaine, and Agatha. It also performs well against Giovanni (with Mega Drain), Lorelei (with Rock Slide) and Lance's Dragon-types, because they will always use Barrier or Agility against it.
Additional Comments: Arbok is held back by its bad Ekans period, especially before it learns Bite. Furthermore, it's reliant on super effective hits to maintain viability later on, so its performance worsens greatly if it's not taught good TMs.

Electabuzz (R)

Availability: Late-game (Power Plant, level 33 or 36).
Typing: Electric gives it a good matchup against Lorelei, although it's useless against Giovanni.
Stats: Outside of decent offenses and 105 Speed (which gives it a 20.50% chance of landing a critical hit) its bulk is unimpressive.
Movepool: Although Electabuzz learns Thunderpunch at level 42, it is still better to give it the Thunderbolt TM, as it otherwise has to rely on Thundershock until then and because Thunderpunch misses on many KOs that Thunderbolt doesn't. Outside of those, Electabuzz can also be taught Psychic, Strength, and Submission through TMs for coverage.
Major Battles: Electabuzz is useful against Lorelei, Bruno, and Lance's Gyarados and Aerodactyl. It will generally do fine against nonspecially bulky like Gengar or Alakazam, though the latter can be handled with Strength.
Additional Comments: Electabuzz comes rather late and is not powerful enough to be useful for what is left of the game, though its high chance of landing a critical hit can compensate for its unremarkable offensive stats.

Farfetch'd (Y)

Availability: Mid-game (Route 11, level 26 or 31).
Typing: Normal / Flying gives it a good matchup against Erika, Koga, and Bruno's Fighting-types, but worsens the matchup against Lorelei. Stats: Farfetch'd stats are rather low and do not hold it for long, thus it has to rely on setup to compensate for them. Its Speed stat gives its Slash around 93% chance to land a critical hit.
Movepool: Farfetch'd greatly appreciates the Body Slam TM in order to hit hard immediately, with Fury Attack at level 15, Double-Edge through TMs, and Slash at level 39 being other alternatives. Swords Dance and Agility at levels 23 and 31 help it sweep, with the former combining well with all STAB moves bar Slash. Its only Flying-type option is Fly through HM.
Major Battles: Farfetch'd generally needs to set up with Swords Dance and potentially Agility in order to sweep any team. This is unreliable at the Pokémon League, as its low bulk makes it hard to set up consistently. Farfetch'd can also just pick off frail targets with Slash critical hits.
Additional Comments: Farfetch'd has low stats and therefore is unable to perform well anywhere without having to set up. Furthermore, even with setup, it is an unreliable choice against the Elite Four, which further limits its usefulness.

Grimer

Availability: Late-game (Pokémon Mansion (1F), level 30 (R), 30 or 34 (B) or 26, 29, 32, or 35 (Y)).
Typing: Poison is not useful for what is left of the game and gives it a weakness against Sabrina and Giovanni.
Stats: Muk has a high HP and Attack, though it's slow and its Special prevents it from using special TMs effectively.
Movepool: Grimer's only STAB move is Sludge at level 37. TM-wise, it can be taught Mega Drain, Thunderbolt, and Fire Blast.
Major Battles: Muk is able to take on physically frail targets with Sludge and on threats it can hit super effectively with TMs. In RB, it is useful against Lance, as his Dragon-types will always use Barrier or Agility against it.
Additional Comments: Grimer comes late and is not particularly useful for what is left of the game. You can catch it directly as a Muk at a higher level with the help of Repels, though its level and rarity vary per game and floor. Grimer is more common in Blue and Yellow than in Red.

Growlithe (Y)

Availability: Late-game (Pokémon Mansion, level 26, 30, 34, or 38 (first floor)).
Typing: Fire does not give Growlithe any advantages at this point of the game and makes it weak to Giovanni. It is also resisted by Lance.
Stats: Arcanine's stats are all around good, most notably having a high Attack and being relatively fast.
Movepool: The line relies entirely on Ember and TMs, as the only useful level-up move Growlithe learns, Flamethrower, comes at level 50. Arcanine's best options from TMs are Body Slam, Double-Edge, Dig, and Fire Blast.
Major Battles: Arcanine can perform well against Blaine and Agatha with Dig and also performs well against Sabrina. It can also pick off kills at the Elite Four with Fire Blast.
Additional Comments: Growlithe comes late and the only way for it to be any good is if you kept the Dig TM for that long to give it to Arcanine. Evolve with Fire Stone immediately, as waiting for Flamethrower at level 50 is not worth it.

Hitmonchan

Availability: Mid-game (Fighting Dojo in Saffron City, Level 30).
Typing: Fighting type allows Hitmonlee to be useful against Lorelei, but is questionable against Sabrina and is not useful for Koga and Agatha.
Stats: Hitmonchan has good Attack, but its Speed is not very high and its bulk (especially on the special side) is very bad.
Movepool: Hitmonchan's most optimal moveset comes from TMs. Its only STAB move is Submission, with Strength acting as coverage. Hitmonchan learns Fire Punch, Ice Punch, and Thunderpunch at levels 33, 38, and 43, but its low Special prevents it from using them effectively. Major Battles: Hitmonchan struggles to sweep any fight outside of the first Giovanni battle. It generally contributes by OHKOing frail targets with STAB Submission, though it's also useful against Lorelei.
Additional Comments: Hitmonchan struggles to perform well against most fights due to its bad bulk and poor movepool. Its only positive traits are that it comes at a high level, its good Lorelei matchup, and its ability to OHKO some Pokémon easily.

Koffing

Availability: Late-game (Pokémon Mansion (1F), level 30 (RB) or 32 (B)) (RB).
Typing: Poison is not useful for what is left of the game and gives it a weakness against Sabrina and Giovanni.
Stats: Weezing is rather slow, though it is rather bulky, particularly on the physical side. Its 85 Special allows it to hit relatively hard.
Movepool: Koffing learns Sludge at level 32 and greatly appreciates Thunderbolt and Fire Blast through TMs. Selfdestruct and Explosion at levels 43 and 53 allow it to weaken difficult opponents later on.
Major Battles: Koffing performs well against Lorelei and Bruno's Fighting-types with Thunderbolt. Lance's Aerodactyl and Gyarados are handled by Thunderbolt, while his Dragon-types only use Agility or Barrier against it, letting Weezing win easily.
Additional Comments: Koffing comes late and is reliant on TMs to be useful. You can also catch it directly as a Weezing with the help of Repels, though its level and rarity vary per game and floor. Note that Koffing is more common in Red than in Blue.

Lickitung (RB)

Availability: Mid-game (trade a Slowbro on Route 18 (RB)).
Typing: Normal is neutral across the whole game, with only Agatha's Ghost-types being immune to it and with Bruno's Fighting-type moves hitting it super effectively.
Stats: Lickitung has below-average stats; it is slow, doesn't take hits well, and generally doesn't hit hard unless it has Swords Dance boosts or is hitting super effectively.
Movepool: Entirely TM-based. Lickitung learns Strength and Earthquake, which can be combined with Swords Dance. It can also be taught Surf for HM utility and to hit opponents like Rhyhorn hard.
Major Battles: In most fights, the only way for it to perform well is to set up Swords Dance and use an appropriate move. Even then, it will often require healing due to below-average bulk and will be unable to sweep tougher opponents like Lorelei and Lance regardless.
Additional Comments: Despite the boosted experience, Lickitung has difficulties performing well in most major fights due to its below-average stats. In Yellow, Lickitung can only be obtained in Cerulean Cave, making it unavailable for the main game there.

Magmar

Availability: Late-game (Pokémon Mansion (3F), level 34) (B).
Typing: At this point of the game, Fire does not provide it with many advantages, with Magmar losing to Lorelei and being resisted by Lance.
Stats: Magmar's stats are largely unimpressive, with its 95 / 85 offenses not helping it for what is left of the game. However, it can outspeed most opponents reasonably with its 93 Speed.
Movepool: Magmar's Ember upgrades to Fire Punch at level 43, with Flamethrower coming at level 55 if you can reach that level. Fire Blast through TMs also provides more power, while Strength, Psychic, and Submission through TMs provide coverage.
Major Battles: Magmar generally doesn't sweep any of the remaining fights, though it can contribute to Sabrina with Strength and handle the end-game with a powerful Fire Blast.
Additional Comments: Magmar comes late and is not very useful for what is left of the game, despite good STAB moves in its learnset.

Moltres

Availability: End-game (Victory Road (2F), level 50, static encounter).
Typing: Fire / Flying provides it with a neutral matchup against whatever is left of the game save for Lorelei, who Moltres is weak to.
Stats: Moltres has an incredibly high Special and the other stats aren't too bad either. However, they are held back by a lack of EVs.
Movepool: Moltres mainly uses Fire Blast and Sky Attack through TMs, with Fire Spin slowly weakening bulky Pokémon.
Major Battles: Moltres can take on most Pokémon at the Pokémon League by hitting them with an appropriate STAB move. However, it will need Ethers and Elixirs to consistently take out more of them.
Additional Comments: While Moltres is very powerful, it doesn't contribute much due to coming extremely late.

Onix

Availability: Mid-game (Rock Tunnel (B1F), level 13 or 17 (RB) or level 14, 18, and 22 (Y)).
Typing: Rock / Ground gives Onix a bad matchup against Erika and Lorelei and a type advantage against Koga, Blaine, and Agatha.
Stats: Onix has an incredibly low Attack, which means that, later on, even super effective moves won't be able to OHKO opponents. Furthermore, its high Defense is not very useful due to its low HP. It is also frail specially.
Movepool: Onix greatly appreciates Dig or Earthquake (preferably the former due to its earlier acquisition) and Rock Slide through TMs. Its only other Rock-type move is Rock Throw at level 19. Bind at level 15 can be used to slowly weaken opponents.
Major Battles: Onix is useful for Koga and Blaine as well as Agatha. It can also defeat Lt. Surge if you obtain it before fighting him. However, don't expect Onix to OHKO its opponents in the later portions of the game.
Additional Comments: Due to its terrible stats, Onix is useful only in few matchups and needs the Dig TM to become usable immediately.

Paras

Availability: Early-game (Mt. Moon, levels 8-12 (RB), 9-13 (Y))
Typing: Bug / Grass is an unfortunate type, only really helping against Misty, Sabrina, and Lorelei, but providing it with three 4x weaknesses. Stats: Parasect has well-rounded stats everywhere except for 30 base Speed, which only enables a 49% critical hit chance with Slash.
Movepool: Paras joins with Scratch, which upgrades to Body Slam through TMs and later Slash at level 39, and learns Stun Spore and Leech Life at levels 13 and 20 and Dig through TMs. Swords Dance through TMs combines well with Body Slam and Dig, while Growth at level 41 can combine with the Mega Drain TM. Spore at level 30 allows Paras to safely set up against the opponent.
Major Battles: Paras has good match-ups against Misty and Erika with Leech Life. If given the Dig TM, it is also excellent against Lt. Surge and can face Agatha. If given the Mega Drain TM, it can also target Giovanni and Lorelei. The Swords Dance TM improves every match-up significantly, although Blaine and the rival still give issues.
Additional Comments: Spore is Paras's selling point, and it helps Paras to get free turns, but it doesn't work well with Paras's low Speed. Ultimately, Paras requires multiple specific TMs to reach its maximum potential. In Yellow, you can also trade a Tangela on Route 18 to get a Parasect, though that Parasect misses out on its best match-ups.

Pidgey

Availability: Early-game (Route 1, level 2-5 (RB) or 2-4 (Y)).
Typing: Normal / Flying gives it a good matchup against Erika, Yellow Koga, and Bruno's Fighting-types. However, it is bad against Brock, Lt. Surge, and Lorelei, as well as against any Rock-type Pokémon.
Stats: Pidgey and Pidgeotto's stats are not very good and you are stuck with them for a while due to Pidgeotto's late evolution. Only after it evolves into Pidgeot do the stats become acceptable, though they fall off later on anyways.
Movepool: Pidgey's Gust and Quick Attack upgrade to Double-Edge through TMs. For a Flying-type move, it can use Fly through HM and later Sky Attack through TMs. It can also be taught support TMs like Reflect and Toxic, as the line doesn't get anything else that is useful.
Major Battles: The line beats Erika, Yellow Koga, and Bruno's Fighting-types just with a Flying STAB move. Outside of those, the line generally contributes by KOing frail opponents, though it can OHKO some threats at the Pokémon League with Sky Attack.
Additional Comments: Despite coming early, Pidgey is limited in its contributions due to its lackluster stats, typing, and movepool. You can also catch it directly as a Pidgeotto in Yellow's Viridian Forest, but it's at a 1% encounter rate, so it's not worth it.

Pinsir

Availability: Mid-game (buy at Rocket Game Corner for 2500 (B) or 6500 (Y) coins; Safari Zone (Central Area (hub)) at level 23 (B) or Area 3 at level 25 (Y)).
Typing: Bug is useless for Pinsir offensively, as it learns no Bug-type moves. Defensively, it gives Pinsir a weakness to RB Koga and Blaine as well as a resistance to Giovanni and Bruno's Fighting-types. Its Speed also makes its Slash a guaranteed critical hit.
Stats: Pinsir has one of the highest Attack stats along with a good Defense and Speed, though its other stats are bad.
Movepool: Pinsir's only viable offensive moves are Strength and Submission through TMs and Slash at level 49. It can combine Strength and Submission with Swords Dance through TMs to sweep opponents. In Yellow, it also learns Bind at level 21 for gradual trapping damge.
Major Battles: Pinsir generally performs well by setting up Swords Dance and then using an appropriate move. This strategy is ineffective against Agatha's Ghost-types, though Pinsir can damage them with Seismic Toss.
Additional Comments: Pinsir's shallow movepool forces it to rely on setup to sweep any fight. Furthermore, it levels up slowly and is a hassle to obtain regardless of the game or method.

Pikachu (Y)

Availability: Early-game (Pallet Town, starter).
Typing: Pure Electric type makes it good for Misty and Lorelei while being weak to Giovanni's Ground types and resisted by Erika.
Stats: Due to not being able to evolve in Yellow, Pikachu's below-60 offenses and paper-thin defenses fall off quickly. Its Speed of 90 gives it a 17.59% chance to land a critical hit though.
Movepool: Thundershock, Thunder Wave, and Quick Attack get Pikachu by until Thunderbolt at level 26. Body Slam via TMs is an upgrade to Quick Attack, but you'll mostly be using Thunderbolt. Light Screen at level 50 can help at the Pokemon League against Lorelei. Seismic Toss through TM can help for Electric and Normal-resistant foes.
Major Battles: Good for Misty and Lorelei, but by the time you reach Koga and onward, Pikachu's stats will be too low to do much to evolved foes.
Additional Comments: Despite learning Thunderbolt naturally, Pikachu's slightly buffed moveset from RB simply isn't enough to compensate for Pikachu's low stats lategame, and it is by far one of the worst starters of all time.

Ponyta

Availability: Late-game (Pokémon Mansion, level 28, 30, 32, or 34) (RB); Mid-game (Route 17, level 28, 30, or 32) (Y).
Typing: Fire only gives Ponyta an advantage against Erika and Koga in Yellow, while in RB, it doesn't provide it with any good matchups.
Stats: Rapidash is fast and has good Attack along with an okay Special, though its other stats are bad.
Movepool: Ponyta's STAB options are Ember, Fire Spin at level 39, and Fire Blast through TMs. Outside of that, its only forms of coverage are Body Slam and Double-Edge via TMs.
Major Battles: In Yellow, it can contribute against Erika with Ember and Koga with Fire Spin. In both games, it is useful against Sabrina and is generally good for KOing frail targets or hitting opponents hard with Fire Blast later on.
Additional Comments: Ponyta is held back greatly by its useless typing and shallow movepool. While it comes earlier in Yellow, it doesn't perform well enough to distinguish itself from its Red and Blue variant tier-wise.

Psyduck (Y)

Availability: Late-game (Route 6, level 15 (Psyduck) or 15 or 20 (Golduck)) (Surfing).
Typing: Water allows Psyduck to perform well against Blaine and Giovanni, but doesn't provide it with any advantages elsewhere.
Stats: Golduck's stats are good, but not very notable, with he highest one being its 95 Special.
Movepool: Golduck relies on Surf and Ice Beam or Blizzard through TMs. It can be taught Dig and Seismic Toss through TMs for coverage.
Major Battles: Golduck beats Blaine, Giovanni, and Bruno with no problems. With an Ice TM, it can handle Lance. It can also potentially contribute against Agatha if it knows Dig.
Additional Comments: Psyduck comes late and underleveled making it inferior to most other Water-types, despite comparable matchups.

Scyther

Availability: Mid-game (buy at Rocket Game Corner for 5500 (R) or 6500 (Y) coins; Safari Zone (Central Area (hub)) at level 23 (B) or Area 2 at level 25 (Y)).
Typing: Bug / Flying is useless offensively due to Scyther learning no Bug moves and Wing Attack (only learned in Yellow) being unhelpful. Defensively, it gives it an advantage against Erika, Giovanni, and Bruno's Fighting-types as well as a weakness to Koga and Blaine.
Stats: Scyther is strong and fast and always lands critical hits with Slash, though it's not very bulky.
Movepool: Scyther's most optimal movepool consists of Slash at level 29, Double-Edge through TMs, and Swords Dance at level 35. In Yellow, it also learns Wing Attack at level 50.
Major Battles: Scyther only performs well by setting up Swords Dance and then using Double-Edge, though it will have to heal sometimes due to recoil. It can also pick off frail targets with Slash, though it's useless against Agatha unless it knows Wing Attack.
Additional Comments: Scyther has a shallow movepool, levels up slowly, and is a hassle to get no matter which method you go for.

Slowpoke (Y)

Availability: Late-game (Seafoam Islands (1F), level 28 or 30) (walking).
Typing: Water makes it useful against Blaine and Giovanni, while Psychic gives it a type advantage against Bruno, and Agatha.
Stats: Slowbro is a bulky Pokémon that is very slow and generally needs Amnesia boosts to hit hard with its 80 Special.
Movepool: Slowbro's offensive options are Surf, Psychic, and Ice Beam or Blizzard through TMs. Amnesia at level 44 allows it to sweep opponents that are not hit super effectively by its moves.
Major Battles: Slowbro handles Blaine, Giovanni, and Bruno with little trouble. With Psychic, it can also help against Agatha if it doesn't get crippled by status moves and can help against Lance with an Ice TM. Amnesia boosts allow it to contribute elsewhere.
Additional Comments: Slowpoke comes underleveled and is hard to train due to its slow growth rate. It also needs Amnesia boosts to perform well in many matchups. You can catch it as a Slowbro directly, but it's at 1% encounter rate and Repel tricking doesn't work here.

Tangela

Availability: Cinnabar Island (RB), in-game trade for a Venonat); Mid-game (Safari Zone, levels 22-27) (Center Area and Area 3) (Y).
Typing: Grass is useful against Lorelei and Giovanni, but lackluster in other spots.
Stats: Tangela has great Defense and good Special, but low Attack and lacking Speed. This can be mitigated with the trade bonus in Red and Blue.
Movepool: Tangela's best STAB moves are Solar Beam and Mega Drain through TMs, which can be combined with Growth at level 48. It can also be taught Swords Dance and Body Slam or Double-Edge through TMs. Sleep Powder at level 39 helps Tangela set up and sweep most opponents. Major Battles: Tangela works well against Giovanni and Lorelei thanks to Growth. With the Swords Dance TM, Tangela's other match-ups improve significantly. Agatha is a notoriously bad match-up without gimmicks like Mimic Dream Eater.
Additional Comments: Tangela can contribute to the end-game thanks to Sleep Powder, but is all around inefficient, as it requires multiple Swords Dance or Growth boosts to sweep.

Venonat

Availability: Mid-game (Safari Zone (Area 2), level 32, caught as Venomoth) (RB); Early-game (Route 24, level 13 or 16) (Y).
Typing: Bug / Poison gives it a type advantage against Erika and RB Koga while resisting Bruno's Fighting-type moves. However, it leaves Venomoth with weaknesses to Sabrina and Blaine, though it also hits the former super effectively.
Stats: It is very weak as Venonat and Venomoth's stats are not very high either, with its highest stats being 90 Special and Speed.
Movepool: In Yellow. Venonat has to manage with Tackle, Confusion at level 11, and Leech Life at level 27 until it evolves. It can also be taught Psychic and Mega Drain through TMs, with Psybeam at level 38 being an alternative for the former. Sleep Powder allows it to cripple an opponent that Venomoth would struggle against otherwise.
Major Battles: Venomoth is good for Erika with Leech Life, while Koga and Bruno are defeated with Psybeam or Psychic. It can contribute against Giovanni with Mega Drain. The other opponents need to be put to sleep, as they can take its attacks easily and wear it down in return.
Additional Comments: Venomoth is not very powerful and relies on sleep in order to beat anything that it doesn't hit super effectively. While Venonat comes earlier in Yellow, its inability to be useful for the earlier fights counterbalances the earlier arrival.

Voltorb (Y)

Availability: Late-game (Power Plant, level 43, caught as an Electrode from fake item balls).
Typing: Electric gives Voltorb a better matchup against Lorelei and a neutral matchup everywhere else bar Giovanni.
Stats: Electrode is the fastest Pokémon in the entire game and has a 27.34% chance of landing a critical hit. Its other stats are not as high, with its Special reaching 80.
Movepool: The line is heavily reliant on the Thunderbolt TM for its best performance. Outside of that, it doesn't have much to go with, other than Selfdestruct and Explosion at levels 27 (as Voltorb) and 50 (as Electrode), though it generally has to weaken the target first to KO it. Support moves like Thunder Wave and Toxic can be taught through TMs.
Major Battles: Electrode performs well against Lorelei and Bruno's Fighting-types and can KO Lance's Gyarados and Aerodactyl. Outside of that, it can generally beat neutral targets that are not too bulky specially, though it is virtually useless against anything that resists Electric.
Additional Comments: Voltorb comes rather late and, due to its unimpressive Special, is not very useful for what is left of the game, though its high chance of landing a critical hit allows it to maintain some viability against bulkier threats.

Zubat

Availability: Early-game (Mt. Moon, levels 6-11).
Typing: Flying / Poison is barely useful offensively, as Golbat learns only one (unhelpful) STAB move. It provides a resistance to Erika and Koga and a weakness to Lt. Surge, Sabrina, and Lorelei.
Stats: Golbat's stats are all around fine for most parts of the game, but fall off at the Pokémon League. The highest one is Speed, which allows it to outspeed the majority of the opponents.
Movepool: Zubat is stuck with Leech Life until it learns Bite at level 15. The only STAB move it learns is Wing Attack at level 32 as a Golbat. TM-wise, Mega Drain makes it useful for KOing threats like Onix and Rhyhorn, while Double-Edge is a stronger alternative to Bite.
Major Battles: Zubat can beat Misty, Erika, and Bruno with no problems. It can also be useful against Yellow Koga, although it should watch out for Psychic. In the other fights, Golbat generally struggles to perform well due to its low-power moves and typing.
Additional Comments: Zubat is a good Poémon for few key fights, but tends to be useless elsewhere.

E-Tier:
The following Pokemon have the lowest level of efficiency. They have little-to-no good matchups or their performance does not compensate for the difficulty of obtaining them.

E-Tier:

Ditto

Availability: Mid-game (Route 13, level 25) (RB); Late-game (Pokémon Mansion (B1F), level 12, 18, or 24) (Y).
Typing: Normal, then whatever it transforms into. Due to its low Speed, it will generally take a neutral hit before transforming.
Stats: Ditto retains its low HP even after transforming. Furthermore, due to it being slow and not having great bulk, it will often take heavy damage before transforming, which further limits its usefulness.
Movepool: Transform, then the movepool of whatever it transformed into. This is particularly bad in Red and Blue, because trainers' movepools are level-up based, which tend to be bad.
Major Battles: Ditto is not a reliable Pokémon for any major fight, as it is very likely for it to take heavy damage before transforming and because whatever it transformed into is not likely to be useful against the other Poémon of the opponent.
Additional Comments: Ditto is the single worst Pokémon one can possibly use in Red, Blue, and Yellow, as it is unable to defeat anything reliably.

Porygon

Availability: Mid-game (buy at Rocket Game Corner for 9999 (RY) or 6500 (B) coins).
Typing: Outside of being threatened by Bruno's Fighting moves and being unable to hit Agatha's Ghost-types, Normal gives it a neutral matchup against every major opponent.
Stats: Porygon's stats are rather low, thus it generally relies on super effective moves to hit hard. Its stats also fall off at the Pokémon League.
Movepool: Its best moves come from TMs, which include Tri Attack, Ice Beam, Blizzard, Thunderbolt, and Psychic. Psybeam at level 23 is an alternative to Psychic if the TM is not available to it.
Major Battles: Porygon's performance is largely dependent on which TMs it is taught; Erika is handled by Ice Beam or Psychic, Koga and Bruno are handled by Psychic, and Giovanni is handled by Ice Beam or Blizzard. At the Pokémon League, due to the opponents' superior stats, Porygon will at most take out few threats with super effective moves.
Additional Comments: Porygon takes a lot of time and resources to be obtained and needs to be taught contested TMs in order for it to perform at an acceptable level.

Untiered:
The following Pokemon are not obtainable in any of the three games before beating the Pokemon League without using glitches or are obtainable only through events.

Untiered

Mew


Mewtwo

 

[DrumstickGaming]

People can reserve writeups now if they like. Squirtle (RB), Charmander and Bulbasaur in A and B tier respectively are already done if you need some examples for inspiration.

 

[Ryota Mitarai]

I will write up some of the mons that (to my knowledge) only I ever used. Also provides more examples.

Also, here's a BBCode template of the write-up format (posting it here for my and anyone else's convenience)

[B]Availability:[/B] content 
[B]Typing:[/B] content
[B]Stats:[/B] content
[B]Movepool:[/B] content
[B]Major Battles:[/B] content
[B]Additional Comments:[/B] content

anyways, here are some entries from me:

Zubat

Availability: Early-game (Mt. Moon, levels 6-11).
Typing: Flying / Poison is barely useful offensively, as Golbat learns only one (unhelpful) STAB move. It provides a resistance to Erika and Koga and a weakness to Lt. Surge, Sabrina, and Lorelei.
Stats: Golbat's stats are all around fine for most parts of the game, but fall off at the Pokémon League. The highest one is Speed, which allows it to outspeed the majority of the opponents.
Movepool: Zubat is stuck with Leech Life until it learns Bite at level 15. The only STAB move it learns is Wing Attack at level 32 as a Golbat. TM-wise, Mega Drain makes it useful for KOing threats like Onix and Rhyhorn, while Double-Edge is a stronger alternative to Bite.
Major Battles: Zubat can beat Misty, Erika, and Bruno with no problems. It can also be useful against Yellow Koga, although it should watch out for Psychic. In the other fights, Golbat generally struggles to perform well due to its low-power moves and typing.
Additional Comments: Zubat is a good Poémon for few key fights, but tends to be useless elsewhere.

Lickitung

Availability: Mid-game (trade a Slowbro on Route 18 (RB)).
Typing: Normal is neutral across the whole game, with only Agatha's Ghost-types being immune to it and with Bruno's Fighting-type moves hitting it super effectively.
Stats: Lickitung has below-average stats; it is slow, doesn't take hits well, and generally doesn't hit hard unless it has Swords Dance boosts or is hitting super effectively.
Movepool: Entirely TM-based. Lickitung learns Strength and Earthquake, which can be combined with Swords Dance. It can also be taught Surf for HM utility and to hit opponents like Rhyhorn hard.
Major Battles: In most fights, the only way for it to perform well is to set up Swords Dance and use an appropriate move. Even then, it will often require healing due to below-average bulk and will be unable to sweep tougher opponents like Lorelei and Lance regardless.
Additional Comments: Despite the boosted experience, Lickitung has difficulties performing well in most major fights due to its below-average stats. In Yellow, Lickitung can only be obtained in Cerulean Cave, making it unavailable for the main game there.

Squirtle (Y)

Availability: Mid-game (from Officer Jenny in Vermillion City after beating Lt. Surge, level 10).
Typing: Water typing gives Squirtle an edge against Blaine, and Giovanni, while giving it a weakness to Erika.
Stats: Squirtle has good well-rounded stats with an emphasis on Defense.
Movepool: Squirtle starts with Water Gun or Bubble Beam through TMs, both of which upgrade to Surf later on via HM. Coverage options in the form of Mega Punch, Dig, and Ice Beam / Blizzard exist, but only an Ice move is really necessary. Strength serves as a more accurate Mega Punch replacement.
Major Battles: Squirtle performs well against Blaine, Giovanni, and Bruno. It is also useful against Lance with Ice Beam or Blizzard (though it may require healing) and for Koga as long as it avoids Sleep Powder. It generally struggles in other matchups, though it can take out some of their Pokémon if it has the appropriate move.
Additional Comments: Squirtle's biggest issues are that it doesn't come very early and that it comes very underleveled, so it has to be grinded to become useful. Outside of that, it is useful in a number of matchups and also provides useful HM utility.

note: yes, I c/ped some of the RB one, I don't see why those parts would be different

Rhyhorn

Availability: Mid-game (Safari Zone, Central Area (hub) at level 25 (RB) or Area 2 at level 25 (Y)).
Typing: Rock / Ground is useful for Koga, Blaine, and Agatha, while being outright bad only against Erika and Lorelei.
Stats: The line hits hard and is bulky physically, but is slow and vulnerable to special attacks.
Movepool: The line greatly appreciates Rock Slide and Dig or Earthquake through TMs. It can also be taught Surf (as a Rhydon) and Strength for coverage and HM utility.
Major Battles: Other than Koga, Blaine, and Agatha, Rhydon is also useful against Giovanni, Bruno, and Sabrina, though it has to watch out for super effective moves from Giovanni and Bruno and is threatened by Sabrina's special attacks. It can also contribute against Lance, though his team in Yellow possesses more super effective moves that threaten Rhydon.
Additional Comments: Rhydon can contribute to many fights with its powerful attacks, but it levels up slowly and evolves late. In Yellow, you can also obtain a Rhydon from an in-game trade at Pokémon Lab in Cinnabar Island for a Golduck, though it skips the Koga matchup and you either have to grind a Psyduck or catch an underleveled Golduck.

I will very likely contribute more in the future, depending on what doesn't get written up.

let me know if I have edit anything in my write-ups.

e: changed "low" to "below-average" on Lickitung

 

[Antihaxxer]

Maybe I miss something, but Drowzee in S tier ? I hope I will understand with the review.
I still have mixed feelings about Bulbasaur in B tier where Razor Leaf Critical Rate can carry the game except against double resistance (and

 

[Xator_Nova]

Clefairy

Availability: Early-game (Mt. Moon, levels 8-12 (RB), 9-13 (Y) )
Typing: Normal has neutral match-ups against every type except for Rock, Ghost and Fighting, which are negative.
Stats: Clefairy has well rounded stats except for a rather low speed, but it's enough for most of the game thanks to the Fast leveling rate.
Movepool: Clefable's level-up movepool is poor, but Clefairy's Sing at Lv13 is a decent support move. Clefable has access to the Mega Punch and Mega Kick TMs, whose power is augmented thanks to STAB. It has access to every special TM to target any weakness. Finally, it can learn Thunder Wave or Reflect.
Major Battles: Misty's Starmie can be defeated by Mega Punch or Seismic Toss. The only Pokémon that Clefable can't 2HKO without Special TMs after that are: Rhydon, Lapras, Haunter, Gengar, Dragonite, and the rival's starter in the final battle.
Additional Comments: Clefairy can evolve at lv13 with the immediately available Moon Stone when it learns Sing. Because of this, it requires minimal, if any, effort to reach its maximum potential through the whole game.

I also want to reserve the grass-types (Bellsprout, Oddish, Exeggcute, Paras, Tangela).

EDIT: Edited with Drums's suggestions

 

[DrumstickGaming]

Clefairy

Availability: Early-game (Mt. Moon, levels 8-12 (RB), 9-13 (Y) )
Typing: Normal has neutral match-ups against every type except for Rock, Ghost and Fighting, which are negative.
Stats: Clefairy has well rounded stats except for a rather low speed, but it's enough for most of the game.
Movepool: Clefable's level-up movepool is poor, but Clefairy's Sing at Lv13 is a decent support move. Clefable has access to the Mega Punch and Mega Kick TMs, whose power is augmented thanks to STAB. It has access to every special TM to target any weakness. Finally, it can learn Thunder Wave or Reflect.
Major Battles: Misty's Starmie can be defeated by Mega Punch or Seismic Toss. The only Pokémon that Clefable can't 2HKO without Special TMs after that are: Rhydon, Lapras, Haunter, Gengar, Dragonite, and the rival's starter in the final battle.
Additional Comments: Clefairy can evolve almost immediately with the Moon Stone available at Mt. Moon. It can also wait until lv13 to learn Sing. Because of this, it requires minimal, if any, effort to reach its maximum potential through the whole game.

I also want to reserve the grass-types (Bellsprout, Oddish, Exeggcute, Paras, Tangela).

Xator_Nova We looked over your analysis and it's pretty good, but AC could use a little more refinement if possible. If you can, try and summarize Clefairy's performance and note its rarity. Maybe you could say "Clefairy can be evolved with Moon Stone at level 13 when it learns Sing." instead of the first two sentences to make it more streamlined.

Also it's fine if you want to reserve the Grass-types. Any help at all is very appreciated, and thanks in advance!

 

[Ryota Mitarai]

Since I am very bored, I will write up Dratini, Porygon and Ditto too, since I doubt anyone else would do so

Porygon

Availability: Mid-game (buy at Rocket Game Corner for 9999 (RY) or 6500 (B) coins).
Typing: Outside of being threatened by Bruno's Fighting moves and being unable to hit Agatha's Ghost-types, Normal gives it a neutral matchup against every major opponent.
Stats: Porygon's stats are rather low, thus it generally relies on super effective moves to hit hard. Its stats also fall off at the Pokémon League.
Movepool: Its best moves come from TMs, which include Tri Attack, Ice Beam, Blizzard, Thunderbolt, and Psychic. Psybeam at level 23 is an alternative to Psychic if the TM is not available to it.
Major Battles: Porygon's performance is largely dependent on which TMs it is taught; Erika is handled by Ice Beam or Psychic, Koga and Bruno are handled by Psychic, and Giovanni is handled by Ice Beam or Blizzard. At the Pokémon League, due to the opponents' superior stats, Porygon will at most take out few threats with super effective moves.
Additional Comments: Porygon takes a lot of time and resources to be obtained and needs to be taught contested TMs in order for it to perform at an acceptable level.

Ditto

Availability: Mid-game (Route 13, level 25) (RB); Late-game (Pokémon Mansion (B1F), level 12, 18, or 24) (Y).
Typing: Normal, then whatever it transforms into. Due to its low Speed, it will generally take a neutral hit before transforming.
Stats: Ditto retains its low HP even after transforming. Furthermore, due to it being slow and not having great bulk, it will often take heavy damage before transforming, which further limits its usefulness.
Movepool: Transform, then the movepool of whatever it transformed into. This is particularly bad in Red and Blue, because trainers' movepools are level-up based, which tend to be bad.
Major Battles: Ditto is not a reliable Pokémon for any major fight, as it is very likely for it to take heavy damage before transforming and because whatever it transformed into is not likely to be useful against the other Poémon of the opponent.
Additional Comments: Ditto is the single worst Pokémon one can possibly use in Red, Blue, and Yellow, as it is unable to defeat anything reliably.

Dratini

Availability: Mid-game (buy at Rocket Game Corner for 2800 (R) or 4600 (B) coins; Safari Zone (Central Area (hub), with Super Rod) (Y)).
Typing: Dragon gives it a bad matchup against Lorelei, though it also resists Erika. It is useless offensively, since Dragon STAB moves do not exist.
Stats: Dragonair's stats are not particularly high, with Dratini's stats being even worse. Dragonite's stats are very high, but, due to late evolution, it is unlikely that the line will get to use them.
Movepool: It learns a variety of TMs, such as Surf, Body Slam, Ice Beam, Blizzard, Thunderbolt, and Fire Blast. It can also utilize the combination of Wrap and Thunder Wave to slowly weaken the opponent.
Major Battles: With Surf, Dratini proves useful for Blaine, Giovanni, and Bruno. Ice Beam can also improve the matchup against Erika and Lance. Thunder Wave + Wrap can be used to put opponents in range for one of its moves to KO them.
Additional Comments: Dratini is not easy to obtain and performs well only in few matchups, with contested TMs being needed to perform better in more. It also levels up slowly. In Yellow, you can reel in a level 15 Dragonair (10% encounter rate) in the Safari Zone's Central Area (hub).

 

[Xator_Nova]

Bellsprout

Availability: Early-game (Route 24 (BY), levels 12-14)
Typing: Useful against Misty and Lorelei, as well as good for Giovanni and resisting Lt. Surge. Not so good against Poison.
Stats: Bellsprout has average defenses but very good attacking stats. Victreebel's 70 base speed allows it to always land criticals with Razor Leaf.
Movepool: Growth can allow Bellsprout to deal with Grass-resisting enemies, while Wrap can prevent enemies from attacking if Bellsprout is faster. It learns Sleep Powder early to gather free turns to boost itself or attack, and then its attacking moves are upgraded to Acid at Lv29 and Razor Leaf at Lv38. Victreebel can learn the Swords Dance TM to sweep enemy teams, the Mega Drain TM is better than Vine Whip, and the Body Slam TM is a superior alternative to Acid. Finally, the Reflect TM can patch Victreebel's average defenses.
Major Battles: Bellsprout is excellent against Misty, Lt. Surge, Giovanni, Lorelei and Bruno. It can also sweep other battles with Sleep Powder and Swords Dance, but struggles without. Agatha is a notoriously bad match-up without gimmicks like Mimic Dream Eater.
Additional comments: It is recommended to hold on evolving with a Leaf Stone from Celadon until Lv38 to learn Razor Leaf. Bellsprout performs excellently with Swords Dance, and can cheese through battles adequately enough without it thanks to Sleep Powder.

Oddish

Availability: Early-game (Route 24 (RY), levels 12-14)
Typing: Useful against Misty and Lorelei, as well as good for Giovanni and resisting Lt. Surge.
Stats: Vileplume has well-rounded stats except for its lackluster 50 speed, which can be alleviated with the badge boost glitch.
Movepool: Absorb can allow Oddish to heal itself while battling, although its lackluster power makes battles slower. It learns Sleep Powder early go gather free turns to attack, and then its attacking moves are upgraded to Acid at Lv29 and Petal Dance at Lv38. Vileplume can learn the Swords Dance TM to sweep enemy teams, the Mega Drain TM is better than Absorb, and the Body Slam TM is a superior alternative to Acid. Finally, the Reflect TM can improve Vileplume's defenses.
Major Battles: Oddish is excellent against Misty. Oddish has also a positive match-up against Lt. Surge, Giovanni and Bruno. It can sweep other battles with Sleep Powder and Swords Dance, but really struggles without. Agatha is a notoriously bad match-up without gimmicks like Mimic Dream Eater.
Additional comments: Since Petal Dance locks the player into an attack, it's recommended to evolve immediately with a Leaf Stone from Celadon and learn the Mega Drain TM. Oddish performs very well with Swords Dance, although its slow speed can get in the way in the lategame, and can cheese through battles thanks to Sleep Powder.

Exeggcute

Availability: Mid-game (Safari Zone, levels 23-27 (RB), 22-26 (Y))
Typing: Psychic is useful against Poison and unresisted by everyone except other Psychics. Grass is good against Lorelei and Giovanni.
Stats: Exeggutor has excellent Special and well-rounded stats everywhere else except speed. The Slow leveling rate worsens the amount of time that Exeggcute needs to catch-up.
Movepool: Exeggcute joins with Hypnosis and Reflect, and it can learn Leech Seed at Lv28. Exeggutor doesn't learn anything by leveling up, but it's compatible with the Strength HM, Psychic TM and Mega Drain TM to deal mixed damage. It can also opt for a combination of Leech Seed with the Toxic TM.
Major Battles: Exeggutor defeats Koga easily with the Psychic TM, helps against Agatha, and can hit Sabrina's Pokémon with Strength. Exeggutor can also target Lorelei with the Mega Drain TM.
Additional comments: Exeggcute can evolve almost immediately at Lv28 with a buyable Leaf Stone soon after it's caught when it learns Leech Seed. Exeggutor's optimal performance relies on the Psychic TM. Without it, it struggles to defeat enemies efficiently, but it can still cheese through battles with Hypnosis or Toxic + Leech Seed.

EDIT: Expanded a bit with summaries at the additional comments

 

[Ryota Mitarai]

hey Xator_Nova (and anyone wanting to write an entry in general), I am not Drumstick, but if you want a small tip, I recommend, in your ACs, to summarize your entries (aka give a short summary as to why this Pokemon is in a particular tier). We did that in BW1 after a GP member recommended us to do so and I would say it turned out greatly. You can check the entries that Drumstick and I have written if you want some inspiration, as well as the BW1 list in my signature.

Your entries are good, though. I can QC them and let you know where you can improve your entries, if you want me to, though if you do, it will happen after I wake up

e: I am also available if you need help with the summaries or you've got more questions

 

[Xator_Nova]

Paras

Availability: Early-game (Mt. Moon, levels 8-12 (RB), 9-13 (Y)), Mid-game (In-game trade for a Tangela (Y), Route 18)
Typing: Bug and Grass gives it three quadruple weaknesses in Fire, Flying and Poison, but they're useful against Water and Grass.
Stats: Parasect has well-rounded stats everywhere except for the worst speed of the fully evolved Pokémon, but this can be mitigated with the badge boost glitch or outsider bonus in Yellow. 30 base Speed only enables 49% critical hit chance with Slash.
Movepool: Paras joins with Scratch, and learns Stun Spore for paralysis and Leech Life soon. Scratch gets upgraded to Slash at Lv39, and Stun Spore gets upgraded to Spore at Lv30, which always sleeps the enemy. Growth is also available at Lv48 for the endgame. Paras has access to the Take Down TM, Body Slam TM and Dig TM, which allow Paras to muscle through enemies before getting Slash; the Mega Drain TM to target Rock-type enemies and functions well with Growth, the Reflect TM to help it endure battles, and the Swords Dance TM to help it reach OHKOs alongside Spore.
Major Battles: Paras has good match-ups against Misty and Erika with Leech Life. If given the Dig TM, it is also excellent against Lt. Surge and can face Agatha. If given the Mega Drain TM, it can also target Giovanni and Lorelei. The Swords Dance TM improves every match-up significantly, although Blaine and the rival still give issues.
Additional comments: Spore is Paras's selling point, and it helps Paras to get free turns, but it doesn't work well with Paras's low speed. Ultimately, Paras requires multiple specific TMs to reach its maximum potential. The in-game trade Parasect misses out on its best match-ups.

Tangela

Availability: Late-game (Route 21 (RB), levels 28-32; Cinnabar Island (RB), in-game trade for a Venonat); Mid-game (Safari Zone (Y), levels 22-27)
Typing: Grass is useful against Lorelei and Giovanni, lackluster in other spots.
Stats: Tangela has great Defense and good Special, but low attack and lacking speed. This can be mitigated with the outsider bonus in Red and Blue, and the badge boost glitch.
Movepool: Tangela's level-up movepool is deficient, with Constrict, Bind and Absorb as its starting moves. It learns Stun Spore at Lv36, Sleep Powder at Lv39, Slam at Lv45 and Growth at Lv48. Its TM compatibility is bizarre: It can use the Body Slam TM, Take Down TM and Swords Dance TM, but its base attack is low. It has a respectable Special, but its best STAB is either the Mega Drain TM or the Solar Beam TM. It has great defenses, but it doesn't learn the Reflect TM. Nevertheless, the outsider bonus is enough to make these moves work adequately.
Major Battles: Tangela works well against Giovanni and Lorelei thanks to Growth. With the Swords Dance TM, Tangela's other match-ups improve significantly. Agatha is a notoriously bad match-up without gimmicks like Mimic Dream Eater.
Additional comments: Tangela's endgame potential is respectable thanks to Sleep Powder, but it involves either raising a deficient Pokémon for multiple levels in the second half of the game, or giving up multiple specific TMs to reach its maximum potential. The in-game trade Tangela is the preferred option to help Tangela catch up quickly and compensate for its deficiencies.

 

[Ryota Mitarai]

writing up more obscure things that only I used. Will likely edit them to fix any issues that they have

Aerodactyl

Availability: Late-game (revive from Old Amber at Pok&eacute'mon Lab in Cinnabar Island, level 30).
Typing: Rock / Flying only provides it with a type advantage against Bruno's Fighting-types and a resistance to Blaine, but worsens the matchup against Lorelei. Rock is also useless offensively, as Aerodactyl learns no Rock-type moves.
Stats: Aerodactyl's Speed is incredibly high and grants it a 25.39% chance of landing a critical hit. Its 105 Attack is also relatively high, though Aerodactyl is not very bulky.
Movepool: Aerodactyl's STAB moves consist of Wing Attack and Fly and later Sky Attack through TMs. Its only other forms of coverage include Bite at level 38, Fire Blast and Double-Edge through TMs, and Hyper Beam at level 54.
Major Battles: Aerodactyl performs well against Sabrina and Blaine. At the Pokémon League, it can OHKO frailer Pokémon like Agatha's Ghost-types and Lance's Dragonair with Sky Attack. The other matchups tend to be bad for Aerodactyl due to its limited movepool and low bulk.
Additional Comments: Aerodactyl comes rather late and is not particularly useful in most of the remaining fights. Old Amber can be obtained in the backroom of the Pewter Museum of Science, though you need Cut to access the room.

Onix

Availability: Mid-game (Rock Tunnel (B1F), level 13 or 17 (RB) or level 14, 18, and 22 (Y)).
Typing: Rock / Ground gives Onix a bad matchup against Erika and Lorelei and a type advantage against Koga, Blaine, and Agatha.
Stats: Onix has an incredibly low Attack, which means that, later on, even super effective moves won't be able to OHKO opponents. Furthermore, its high Defense is not very useful due to its low HP. It is also frail specially.
Movepool: Onix greatly appreciates Dig or Earthquake (preferably the former due to its earlier acquisition) and Rock Slide through TMs. Its only other Rock-type move is Rock Throw at level 19. Bind at level 15 can be used to slowly weaken opponents.
Major Battles: Onix is useful for Koga and Blaine as well as Agatha. It can also defeat Lt. Surge if you obtain it before fighting him. However, don't expect Onix to OHKO its opponents in the later portions of the game.
Additional Comments: Due to its terrible stats, Onix is useful only in few matchups and needs the Dig TM to become usable immediately.

Caterpie

Availability: Early-game (Virdian Forest, level 3 (R), 3-5 (B), or 3-6 (Y)).
Typing: Bug / Flying is only useful for resisting Erika. It gives Butterfree a weakness to RB Koga, Lt. Surge, and Blaine and is useless offensively, as Butterfree doesn't learn STAB moves at all.
Stats: Butterfree's stats are very high for the earlier portions of the game, though as the game goes on, they will start to fall off.
Movepool: Butterfree learns Confusion and Sleep Powder at levels 12 and 17 in RB and levels 10 and 15 in Yellow. Confusion upgrades to Psybeam at level 32 (RB) or 34 (Y) or to Psychic through TMs. Mega Drain through TMs provides coverage against Rock-types.
Major Battles: With a Psychic move, it can beat Koga, Erika, and Bruno with little difficulty. Against the rest, it typically has to put them to sleep with Sleep Powder and take a lot of time KOing them with Psybeam or Psychic. In Yellow, it is also useful for Brock due to learning Confusion earlier.
Additional Comments: Butterfree is good for few fights, but its low stats force it to put most opponents to sleep and slowly take them out, which generally takes a lot of time to pull off.

Meowth

Availability: Early-game (Route 5, levels 10, 12, 14, or 16) (B).
Typing: Normal is neutral against everything, except against Agatha's Ghost-types, and also fears Fighting-type moves from Bruno.
Stats: Persian's high 115 Speed gives it a 22.46% chance of landing a critical hit and ensures that Slash will always result in one as well. The other stats are not particularly high and fall off at the Pokémon League.
Movepool: Its STAB moves are Bite at level 12, Body Slam or Double-Edge through TMs, and Slash at level 51. Pay Day at level 17 is a good way to earn extra money. Coverage includes Water Gun / Bubble Beam and Thunderbolt through TMs, though only a Water move is really needed.
Major Battles: Persian rarely achieves a reliable sweep and is instead better off outspeeding and KOing frailer threats like the Abra line, though it can perform well against Lorelei with Slash. It also performs well against Giovanni with Bubble Beam or Water Gun.
Additional Comments: Meowth's biggest contributions are its ability to generate extra money and the ability to outspeed and KO frail Pok&ecute;mon.

 

[DrumstickGaming]

Okay, we are caught up on analyses right now and they are slotted into the list above! Thanks very much to Nova for your help. If Nova or anyone else wants to reserve analyses next, lemme know ASAP. Otherwise production is going quite smoothly. Oh, and if there are any typos also let us know.

Any help is appreciated greatly...you'd be surprised how much work it takes to get these summaries looking good and reading well.

I think Ryota and I are probably going to tackle the rest of the S tiers next.

Edit: We are done with S-tiers as of now.

 

[Ryota Mitarai]

Nidoran-M

Availability: Early-game (Route 22, levels 2-4 (R), 3-4 (B), or 2 or 4 (Y)).
Typing: Outside of worsening the matchup against Misty, Sabrina, and Lorelei, Poison / Ground is excellent, because it gives Nidoking a type advantage against Lt. Surge, RB Koga, Blaine, and Agatha, while also providing it with a handy immunity to poisoning.
Stats: Nidoking's stats are all around good; it can reasonably outspeed most of the opponents and can run mixed sets viably.
Movepool: Nidoking learns a variety of TMs, with Earthquake and Surf being the only ones that are needed for an excellent performance. Other TMs include Seismic Toss, Thunderbolt, Ice Beam, Blizzard, Water Gun, and Bubble Beam. Level-up wise, Nidoran-M learns Horn Attack at level 8 and, in Yellow, Double Kick at level 12, and Nidoking learns Thrash at level 23.
Major Battles: Nidoking performs well in most matchups just with Earthquake and Surf, with Misty and Lorelei being the only opponents that really trouble it. In Yellow, it is also good for Brock due to learning Double Kick earlier. Other TMs can easen some matchups for Nidoking, but are generally not needed for a great performance.
Additional Comments: Early arrival and excellent performance with just Earthquake and Surf, while also not needing other TMs to perform well, make Nidoran-M one of the best options for an efficient run of Pokémon Red, Blue, and Yellow. Evolve with Moon Stone as soon as possible, as Nidorino doesn't learn anything useful by level. Note that Nidoking does not learn Dig in RBY.

Nidoran-F

Availability: Early-game (Route 22, levels 3-4 (R), 2-4 (B), or 2 or 4 (Y)).
Typing: Outside of worsening the matchup against Misty, Sabrina, and Lorelei, Poison / Ground is excellent, because it gives Nidoqueen a type advantage against Lt. Surge, RB Koga, Blaine, and Agatha, while also providing it with a handy immunity to poisoning.
Stats: Nidoqueen's stats are all around good; it can reasonably outspeed most of the opponents and can run mixed sets viably.
Movepool: Nidoqueen learns a variety of TMs, with Earthquake and Surf being the only ones that are needed for an excellent performance. Other TMs include Seismic Toss, Thunderbolt, Ice Beam, Blizzard, Water Gun, and Bubble Beam. Level-up wise, Nidoran-F learns Double Kick at level 12 in Yellow and Nidoqueen learns Body Slam at level 23.
Major Battles: Nidoqueen performs well in most matchups just with Earthquake and Surf, with Misty and Lorelei being the only opponents that really trouble it. In Yellow, it is also good for Brock due to learning Double Kick earlier. Other TMs can easen some matchups for Nidoqueen, but are generally not needed for a great performance.
Additional Comments: Early arrival and excellent performance with just Earthquake and Surf, while also not needing other TMs to perform well, make Nidoran-F one of the best options for an efficient run of Pokémon Red, Blue, and Yellow. Evolve with Moon Stone as soon as possible, as Nidorina doesn't learn anything useful by level. In Red and Blue, you can also trade a Nidoran-M or Nidorino for a Nidoran-F or Nidorina in the Underground between Route 5 and 6 and Route 11, respectively. Note that Nidoqueen does not learn Dig in RBY.

Mr. Mime

Availability: Early-game (trade an Abra (RB) or a Clefairy (Y) in a house on Route 2).
Typing: Psychic is only resisted by Sabrina and neutral at worst against the other major opponents.
Stats: Mr. Mime has a good Special and is relatively fast, having a 17.59% chance of landing a critical hit. However, it has a low HP and Defense.
Movepool: Confusion upgrades to Psychic through TMs and Mr. Mime can also be given the Thunderbolt TM to improve the Lorelei matchup. Thunder Wave + Seismic Toss are Mr. Mime's best way of dealing with other Psychic-types. Support moves include Barrier, Light Screen at level 23, and Substitute at level 47, while Confuion can be kept as a secondary STAB to not waste Psychic's PP.
Major Battles: In most fights, using a Psychic move is more than enough for a good performance, with only Psychic-types requiring Thunderbolt or Seismic Toss to be defeated.
Additional Comments: Mr. Mime's early arrival, typing, offensive stats, and traded experience make it an all-around solid choice for any efficient run of the games.

Poliwag

Availability: Mid-game (Celadon City, level 23 (RB); Route 23, level 30 or 40 (Y)) (Super Rod, reeled in as Poliwhirl).
Typing: Water makes Poliwrath useful against Blaine and Giovanni, while Fighting gives it a better matchup against Lorelei. The typing is not particularly good for Sabrina and Lance.
Stats: Most of Poliwrath's stats are okay, but its Special is not particularly high and thus will need Amnesia boosts to hit neutral targets harder.
Movepool: Poliwrath mainly uses Surf and Ice Beam or Blizzard, with Submission through TMs being its only Fighting STAB. Poliwhirl learns Hypnosis at level 16 and Amnesia at level 41, which help it sweep opponents.
Major Battles: Poliwrath easily beats Blaine, Giovanni, and Bruno and can also contribute against Erika and Lance with Ice Beam. However, it will often need Amnesia boosts and sometimes Hypnosis in order to achieve a sweep.
Additional Comments: Poliwrath is very reliant on Amnesia boosts to perform well in most fights. In Yellow, you can fish on Route 23 after defeating Erika, though you could potentially fish for one at Route 22 for an earlier, but underleveled Poliwhirl. Also note that level 40 Poliwhirl are rather uncommon, so it may take you some time to find one. Evolve with Water Stone at level 41 after learning Amnesia.

those are already in the OP, we discussed it with DMS privately, posting them for reference

 

[Ryota Mitarai]

Machop line for both games and Magnemite for both games. Some parts are c/ped because they are the same for both versions (and it doesn't make much sense to be different, really)

Machop (RB)

Availability: Mid-game (Rock Tunnel, level 15 or 17).
Typing: Fighting allows the line to be useful against Lorelei, but is terrible against Sabrina and is not particularly useful for Koga.
Stats: The line's only notable stat is their Attack, which is particularly high for Machoke and very high for Machamp. Machoke and Machamp's Speed give their Karate Chop around 70% and 78% chance to land a critical hit, respectively.
Movepool: The line's only STAB moves are Low Kick at level 20 and Submission through TMs, with the former being preferred. The line greatly appreciates Rock Slide and Dig or Earthquake through TM. Karate Chop is useful for beating route trainers without wasting other moves' PP, but isn't useful for most major fights.
Major Battles: With Rock Slide and a Ground TM, the line performs well against Koga, Blaine, and Agatha, while Fighting STAB lets it handle Lorelei and most of Giovanni's Pokémon. It can also beat Lance's Dragon-types, as they will always use Agility or Barrier against it.
Additional Comments: Machop comes rather underleveled and is rather weak, so it takes some effort to evolve it. Furthermore, its evolutions perform strongly only when taught the correct TMs. Both Machoke and Machamp have a similar performance, so even if you cannot trade to evolve, you won't generally miss out on too much.

Machamp (Y)

Availability: Mid-game (trade a Cubone in the Underground between Route 5 and Route 6).
Typing: Fighting allows the line to be useful against Lorelei, but is terrible against Sabrina and is not particularly useful for Koga.
Stats: Machamp has a very high Attack, although its other stats are not particularly notable. Its Speed stat gives its Karate Chop around 78% chance to land a critical hit.
Movepool: Machamp's only STAB moves are Low Kick (with which it starts) and Submission through TMs, with the former being preferred. Machamp greatly appreciates Rock Slide and Dig or Earthquake through TM. Karate Chop is useful for beating route trainers without wasting other moves' PP, but isn't useful for most major fights.
Major Battles: With Rock Slide and a Ground TM, the line performs well against Koga, Blaine, and Agatha, while Fighting STAB lets it handle Lorelei and most of Giovanni's Pokémon.
Additional Comments: Machamp's biggest flaw is the reliance on TMs to perform greatly, but is otherwise a strong Pokémon that can be trained easily due to traded experience. You can also catch a Machop in Rock Tunnel for a slightly earlier arrival, but it doesn't provide any notable advantages over the traded one. Note that you receive it as a Machoke from the trade, which then proceeds to evolve.

Magnemite (RB

Availability: Late-game (Power Plant, level 21 or 23).
Typing: Electric makes Magneton useful for Lorelei and some of Lance's Pokémon, but makes it useless against Giovanni.
Stats: Magneton has one of the highest Special stats in the whole game. However, its other stats are not as high, though 95 Defense allows Magneton to be somewhat bulky.
Movepool: Magneton is viable only when taught Thunderbolt through TMs. Outside of that, it doesn't possess any great moves, so it can either be taught support moves like Thunder Wave, Toxic, and Reflect through TMs or moves with situational use, such as Double-Edge and Thunder through TMs.
Major Battles: Magneton performs very well against Lorelei and reasonably well against any other opponent that does not resist Electric, though Pokémon with high Specials, such as Gengar and Alakazam, tend to avoid 2HKOs from it.
Additional Comments: Magneton can beat many neutral opponents easily with its high Special and Thunderbolt, but it comes rather late and has a shallow movepool. You can also catch it as a Magneton at level 32 or 35, though it's at 10% encounter rate, so Repel tricking is needed to find it fast.

Magnemite (Y)

Availability: Mid-game (Route 10, level 16, 18, 20, or 22).
Typing: Electric makes Magneton useful for Lorelei and some of Lance's Pokémon, but makes it useless against Giovanni and not very useful against Erika.
Stats: Magneton has one of the highest Special stats in the whole game. However, its other stats are not as high, though 95 Defense allows Magneton to be somewhat bulky.
Movepool: Magneton is viable only when taught Thunderbolt through TMs. Outside of that, it doesn't possess any great moves, so it can either be taught support moves like Thunder Wave, Toxic, and Reflect through TMs or moves with situational use, such as Double-Edge and Thunder through TMs.
Major Battles: Magneton performs very well against Lorelei and reasonably well against any other opponent that does not resist Electric, though Pokémon with high Specials, such as Gengar and Alakazam, tend to avoid 2HKOs from it.
Additional Comments: Magneton is a strong Pokémon that can beat most neutral targets easily. Its biggest flaw is its shallow movepool, making it useless against any Pokémon that resists Electric.

e: DMS requested me to do a bunch more:

Mankey (R)

Availability: Early-game (Route 5, level 10, 12, 14, or 16).
Typing: Fighting lets Mankey be useful against Lorelei, but is terrible against Sabrina and is not particularly useful for Koga.
Stats: Primeape is fast and has a high Attack, though it's not very bulky. Both Mankey and Primeape are fast enough to always land critical hits with Karate Chop.
Movepool: Scratch upgrades to Karate Chop at level 15. Primeape's only Fighting STAB is Submission through TMs. It performs best with Dig through TMs and also appreciates the Rock Slide and Seismic Toss TMs.
Major Battles: If taught Dig, the line performs well against Lt. Surge, Koga, Blaine, and Agatha, with Rock Slide or Submission helping against Lorelei. Blaine can also be handled by Rock Slide.
Additional Comments: Mankey is reliant on the Dig TM to perform well against most fights. However, should it get access to that TM, it will have a good performance.

Omanyte

Availability: Late-game (revive Helix Fossil at Pokémon Lab on Cinnabar Island, level 30).
Typing: Water typing gives it a type advantage against Blaine and Giovanni and is resisted by Lorelei. Rock typing does not have offensive use, as the line does not learn any Rock-type moves.
Stats: Omastar has great Defense and Special, though, on the other hand, it is very slow.
Movepool: Omastar mostly uses Surf and Ice Beam or Blizzard through TMs. It doesn't learn anything else that's notable, outside of Hydro Pump at level 49 and support moves from TMs like Reflect and Toxic.
Major Battles: Omastar performs well against Blaine, Giovanni, and Bruno, with Ice Beam and Blizzard helping it against Lance. The other opponents tend to have Pokémon with high Special, allowing them to withstand Omastar's attacks.
Additional Comments: Omanyte is strong, but the late arrival and the abundance of specially bulky Pokémon in the late-game greatly hold it back.

Cubone

Availability: Mid-game (Poémon Tower, level 20 (all games) or 22 (RB)).
Typing: Ground is useful for RB Koga, Blaine, and Agatha, but bad for Erika and Lorelei.
Stats: Marowak's stats, outside of 110 Defense, are not particularly high; it is rather slow and its 80 Attack isn't particularly high. Its low Special also prevents it from using the special TMs it can learn.
Movepool: Although Cubone starts with Bone Club, it vastly prefers Dig or Earthquake through TMs due to their higher power and accuracy. It also learns Bonemerang at level 48 as Marowak as a replacement, though it comes rather late. As it cannot use special TMs like BubbleBeam, Ice Beam, and Fire Blast due to its low Special, it is limited only to Strength for physical coverage.
Major Battles: Marowak is typically useful only against Ground-weak opponents like RB Koga, Blaine, and Agatha and generally struggles to OHKO the other opponents due to its unimpressive Attack.
Additional Comments: Despite learning Ground moves by level, they are either weak or come late, thus Cubone is still reliant on the Ground TMs to be useful. Furthermore, even with them, Cubone is generally limited in its conributions when it doesn't have a type advantage. In Yellow, Cubone is available from the fifth floor onwards.

Jigglypuff (RB)

Availability: Early-game (Route 3, level 3, 5, or 7).
Typing: Outside of Agatha and Bruno's Fighting-types, Normal gives Wigglytuff a neutral matchup against every major opponent.
Stats: Wigglytuff has an incredibly high HP. Its Attack is good for the earlier portions of the game, but falls off later on. Its low Special means that it can only hit hard with the many special TMs it learns when it hits super effectively.
Movepool: Outside of Sing, its movepool is entirely TM-based. It should be taught Mega Punch, which then upgrades to Body Slam or Strength, and Seismic Toss to handle bulkier opponents. Other TMs include Ice Beam, Blizzard, Thunderbolt, Psychic, Water Gun, and BubbleBeam.
Major Battles: Wigglytuff handles Misty, Lt. Surge, and most of the Elite Four with Seismic Toss and potentially Sing, with Normal STAB dealing with Sabrina and TMs handling the other opponents. As the game goes on, it will need to put more opponents to sleep to compensate for its low stats.
Additional Comments: While most of its stats are not very high, Wigglytuff can still perform well against most fights thanks to high HP, Sing, and wide TM learnset. It is also in the Fast experience group, so it is easy to train and can outlevel opponents to compensate for its low stats. Jigglypuff should be evolved as soon as possible with Moon Stone due to not learning anything useful by level.

Jigglyupuff (Y)

Availability: Early-game (Route 5, level 3, 5, or 7).
Typing: Outside of Agatha and Bruno's Fighting-types, Normal gives Wigglytuff a neutral matchup against every major opponent.
Stats: Wigglytuff has an incredibly high HP. Its Attack is good for the earlier portions of the game, but falls off later on. Its low Special means that it can only hit hard when it hits super effectively. Movepool: Outside of Sing, its movepool is entirely TM-based. It should be taught Mega Punch (which later upgrades to Body Slam or Strength) and Seismic Toss to handle bulkier opponents. Other TMs include Ice Beam, Blizzard, Thunderbolt, Psychic, Water Gun, and BubbleBeam.
Major Battles: Wigglytuff handles Lt. Surge, and most of the Elite Four with Seismic Toss and potentially Sing, with Normal STAB dealing with Sabrina and TMs handling the other opponents. If you sequence break, it can also be useful for Misty with Seismic Toss, though you have to grind Wigglytuff with whatever you have available. It will have to put opponents to sleep quite often, as many major opponents can hit it hard and withstand its attacks.
Additional Comments: Due to Yellow's harsher level curve, Wigglytuff's stats generally do not hold it for long. Even then, it can still perform well in many fights due to high HP, Sing, and wide TM learnset. It is also in the Fast experience group, so it is easy to train and can outlevel opponents to compensate for its low stats. Jigglypuff should be evolved as soon as possible with Moon Stone due to not learning anything useful by level.

 

[Ryota Mitarai]

Mankey (Y)

Availability: Early-game (Route 22, level 3 or 5).
Typing: Fighting lets Mankey be useful against Brock and Lorelei, but is terrible against Sabrina and is not particularly useful for Koga.
Stats: Primeape is fast and has a high Attack, though it's not very bulky. Both Mankey and Primeape are fast enough to always land critical hits with Karate Chop.
Movepool: Scratch upgrades to Karate Chop at level 15. Primeape's best Fighting STAB is Low Kick at level 9. It performs best with Dig through TMs and also appreciates the Rock Slide and Seismic Toss TMs.
Major Battles: Mankey is one of the only Pokémon that can beat Brock in Yellow. In addition, it beats Lt. Surge just with Karate Chop and is good against Lorelei thanks to Low Kick, while Dig lets it handle Blaine and Agatha and Rock Slide helps against Koga.
Additional Comments: Mankey is a useful Pokémon in some very key matchups. However, it needs the Dig TM to achieve its best performnce, although it's a solid team member if it gets access to it.

Pikachu (RB)

Availability: Early-game (Viridian Forest, level 3 or 5).
Typing: Electric is useful for Misty and Lorelei, though rather useless against Brock, Erika, and Giovanni.
Stats: Raichu is very fast, having a 19.58% chance of landing a critical hit. Its Attack and Special are also good, though Raichu is frail physically.
Movepool: Thundershock upgrades to Thunderbolt through TMs. Pikachu also learns Thunder Wave at level 9. Its coverage is rather poor, with the only viable alternatives being Seismic Toss and Body Slam or Double-Edge through TMs.
Major Battles: Pikachu is useful against Misty's Starmie, despite not beating it, by paralyzing it and then weakening it with Thundershock. It can also beat Lt. Surge's Raichu with a combination of Thunder Wave and Seismic Toss. After it learns Thunderbolt, it performs well against most opponents that don't resist Electric, with Thunder Wave helping against Special walls like Alakazam and Gengar.
Additional Comments: Pikachu is a handy Pokémon that can contribute in many fights by defeating opponents with Thunderbolt or spreading paralysis. However, Electric tends to be resisted quite often and Pikachu doesn't possess the means to get past resistant opponents efficiently. Evolve with Thunderstone immediately, as Pikachu does not learn any useful moves by level at that point.

Seel

Availability: Late-game (trade a Ponyta (RB) or Growlithe (Y) in Cinnabar Island's Pokémon Lab).
Typing: Water makes the line useful against Blaine and Giovanni, while Ice gives it a valuable advantage against Lance. However, Water / Ice is not particularly useful against Lorelei.
Stats: Dewgong's stats are good, for most parts, though none of them is particularly high, with the highest being its 95 Special, though it can easily outlevel opponents with traded experience to compensate for that.
Movepool: Dewgong mainly uses Surf and Ice Beam or Blizzard through TMs. Strength is its best option against special attackers. Its fourth move can be a secondary STAB, such as Aurora Beam at level 35 or BubbleBeam through TMs, in order to not waste the stronger moves' PP.
Major Battles: Dewgong easily beats Blaine, Giovanni, and Bruno, while STAB Ice Beam or Blizzard handle Lance with little issue. It can also perform reasonably well against Sabrina with Strength.
Additional Comments: While Seel comes rather late, it makes up for that with its traded experience and Ice typing, which gives it an easy matchup against Lance. Players of Yellow will receive it directly as a Dewgong, instead of a Seel, upon performing the in-game trade.

Spearow

Availability: Early-game (Route 22, level 3 or 5 (RB) or level 2, 4, or 6 (Y)).
Typing: Flying is useful against Erika, Yellow Koga, and Bruno's Fighting-types, with Normal giving it a neutral matchup almost everywhere else. However, the typing is bad against Brock, Lt. Surge, and Lorelei.
Stats: Fearow is rather fast, having a 19.53% chance of landing a critical hit. Its Attack is also rather good, though Fearow is not very bulky.
Movepool: Spearow starts off with Peck, which upgrades to Drill Peck at level 34 as Fearow. Its Normal STAB is Fury Attack at level 15 and later Double-Edge through TMs. As Fearow lacks coverage, its other moves could be support ones like Leer and Growl or Fly through HMs for transportaion.
Major Battles: Fearow performs well against Erika, Koga, Bruno's Fighting-types, and Agatha with Flying STAB. Normal STAB lets it handle Sabrina easily. Against the rest, it can either easily KO frail threats or support teammates with Growl and Leer.
Additional Comments: Spearow comes early and is useful in many matchups. However, it is virtually useless against Rock-type Pokémon and struggles against physically bulkier threats, unless it's hitting them super effectively.

Staryu

Availability: Mid-game (Route 19, level 15 (RB) or level 20 (Y)) (Super Rod).
Typing: Water gives it a type advantage against Blaine and Giovanni, while Psychic makes it useful against Koga, Bruno, and Agatha.
Stats: Starmie's high 115 Speed, which gives it a 22.46% of landing a critical hit, combines well with its good 100 Special. Its only partcularly low stat is 60 HP.
Movepool: Starmie's movepool is entirely TM-based. It learns Surf, Psychic, Thunderbolt, Ice Beam, and Blizzard. The more TMs it has access to, the more good matchups it will have.
Major Battles: Starmie can handle virtually every single opponent that it can face if it has the correct TMs; Thunderbolt handles Lorelei, Ice TMs handle Lance, and Surf and Psychic handle the rest. Sabrina is the only major opponent that is not weak to any of Starmie's moves.
Additional Comments: Staryu is a notable Water-type due to its large TM learnset, which allows it to handle more opponents than the other Water-types. However, the earlier Staryu comes underleveled and is a hassle to grind due to its slow growth rate. You can also catch Staryu at Seafoam Islands at a higher level (level varies per floor and method of encounter), though it misses on the Koga matchup and will still be at a lower level than your team, in most cases. Evolve with Water Stone immediately.

those are already in the first post with slight edits, posting them for refernece again.

We are planning on tackling the rest of C soon

 

[Ryota Mitarai]

Drumstick and I went ahead and wrote up the rest of the Pokemon. I am posting my write-ups for reference here, though we edited some of them when they were added to the OP:

lots of write-ups

Krabby

Availability: Mid-game (Vermillion City, level 15 (RB); Route 10, level 25, caught as Kingler (Y)) (Super Rod);
Typing: Water make Krabby useful against Blaine and Giovanni, but is not useful against Erika, Lorelei, and Lance.
Stats: Kingler has one of the highest Attack stats in the entire game, although its low Special prevents it from using STAB moves effectively. However, its base 75 Speed guarantees critical hits on its Crabhammer, which can compensate for that. Its HP is also very low, though its Defense is high.
Movepool: The line's most notable move is Crabhammer at level 42, which is the only STAB move that Kingler can hit hard with. It can also sweep with Swords Dance and Strength through TMs. Surf and Ice Beam can be taught via TMs, though Kingler doesn't use them very effectively.
Major Battles: Kingler is good for Blaine, Giovanni, and Bruno just with Crabhammer. Sabrina can be handled with Strength as long as you are not outsped or hit constantly. The other matchups, bar Agatha, can be swept with Swords Dance and Strength.
Additional Comments: Due to its low Special, Kingler cannot put most of its STAB moves, aside from Crabhammer, and coverage moves to great use, so it has to rely on set up to perform well against major opponents that are not weak to Water. Players of Blue and Yellow can also catch Krabby or Kingler at a higher level at Seafoam Islands, though, depending on the level it's caught at,, it will have to catch up with your team anyways. Players of Red and Blue can also fish for Kingler on Route 23 after obtaining the Rainbow Badge.

Goldeen

Availability: Mid-game (Fuchsia City, level 23 (RB); Route 24, level 30 (Y)) (Super Rod).
Typing: Water provides it with a good matchup against Blaine and Giovanni, but isn't too useful elsewhere.
Stats: Seaking's stats are all around okay, but not particularly high. It can run mixed sets to a reasonable viability.
Movepool: Seaking mostly uses Surf and Ice Beam through TMs, though it can be given the Double-Edge TM for physical coverage. Waterfall at level 39 can act as a secondary STAB move to Surf to preserve PP.
Major Battles: Outside of Blaine and Giovanni, Seaking also handles Bruno easily. With Double-Edge, it also has a good matchup against Sabrina.
Additional Comments: Goldeen can contribute to some matchups thanks to its Water typing and ability to run mixed sets, though it generally doesn't stand out from the other Water-types in the game.

Horsea

Availability: Mid-game (Route 19, level 15 (RB); Route 12, level 20 or 25 (Y)) (Super Rod).
Typing: Water gives it an advantage against Bruno and Giovanni and a neutral matchup elsewhere, bar Erika and Lorelei.
Stats: Seadra's stats are mostly good, as it's able to outspeed many opponents and hit them rather hard, though its HP is low.
Movepool: Seadra's movepool isn't huge, consisting of Surf and Ice Beam or Blizzard through TMs and Hydro Pump at level 52. It can use Smokescreen to cripple a more difficult opponent and potentially beat it or assist a teammate.
Major Battles: Beats Blaine, Giovanni, and Bruno with Surf, while Lance can be handled with an Ice TM. Erika can also be weakened with Ice Beam, though the line isn't doing much there anyways.
Additional Comments: Horsea contributes mainly with its Water typing and good stats, though it's rather useless in many matchups. Players of Red and Blue can catch it directly as Seadra on Route 23 after obtaining Rainbow Badge, with players of Red also being able to catch it at a higher level at Seafoam Islands with the help of Repels. Players of Yellow can also reel in a Seadra at level 25 or 35, though it's at a 30% encounter rate, so it may take some time to catch the level 35 one.

Kabuto

Availability: Late-game (revive Dome Fossil at Cinnabar Island's Pokémon Lab, level 30).
Typing: Water is useful for Blaine and Giovanni and is neutral everywhere, except against Lorelei. Rock is useless, as the line does not learn any Rock-type moves.
Stats: Kabutops has a high Attack and is relatively fast, allowing it to always land critical hits with Slash. However, its 70 Special is not really high, so it will struggle to hit hard with STAB moves.
Movepool: Kabutops's best STAB move is Surf and can be combined with Ice Beam or Blizzard through TMs. It can also sweep teams with Swords Dance and Double-Edge through TMs. Slash at level 39 allows the line to beat Route trainers rather quickly.
Major Battles: Kabutops performs well against Bruno, Giovanni, and Bruno, with Swords Dance and Double-Edge allowing it to sweep the others, except Agatha. It can also be useful against Lance with an Ice TM.
Additional Comments: Kabuto comes rather late, though it can take on more opponents than most Water-types if it takes the time to set up Swords Dance, though it will have to heal often if using Double-Edge.

Lapras

Availability: Mid-game (from an NPC on Silph Co.'s 7th floor, after defeating rival, level 15).
Typing: Water makes it useful for Blaine and Giovanni, while Ice gives it a type advantage against Lance. The typing is not very useful against Lorelei.
Stats: Lapras is very bulky due to its 135 HP and also has a relatively good Special. However, it is not really fast, so it will be outsped from time to time.
Movepool: Lapras uses Surf from HM and Ice Beam at level 38. Sing at level 16 allows it to beat opponents it wouldn't be able to beat otherwise. Lapras can also be taught Thunderbolt and Psychic through TMs, the former improving the matchup against Lorelei. Body Slam at level 25 provides physical coverage.
Major Battles: Lapras handles Blaine, Giovanni, Bruno, and Lance just with STAB moves. Sabrina can also be handled to some extent with Body Slam, while Lorelei is a good matchup with Thunderbolt.
Additional Comments: Lapras is a strong Pokémon with a good movepool, but it comes very underleveled and is a hassle to train due to its slow growth rate. Furthermore, you need to ensure you have enough route trainers so Lapras can be trained efficiently, so you may have to fight your rival at Silph Co. as soon as possible.

Psyduck (RB)

Availability: Mid-game (Route 24, level 15) (Super Rod);
Typing: Water allows Psyduck to perform well against Blaine and Giovanni, but doesn't provide it with any advantages elsewhere.
Stats: Golduck's stats are good, but not very high. The highest one is its 95 Special.
Movepool: Golduck is mainly relying on Surf and Ice Beam or Blizzard through TMs. It can be taught Dig and Seismic Toss through TMs for coverage.
Major Battles: Beats Blaine, Giovanni, and Bruno with no problems. With an Ice TM, it can handle Lance, as well as Erika with Ice Beam only. It can also potentially contribute against Agatha if it knows Dig.
Additional Comments: The line contributes mostly with Water typing and good stats, but is not particularly amazing. Furthermore, Psyduck is rather weak and comes underleveled. Golduck can also be caught at Seafoam Islands at a higher level, though that one comes later.

Shellder

Availability: Mid-game (Vermillion City, level 15 (RB); Route 18, level 20, 30, or 40 (Y)) (Super Rod);
Typing: Water makes the line good against Blaine and Giovanni, while Ice gives it a type advantage against Lance. The typing is useless against Lorelei.
Stats: Cloyster has an okay Special stat and a really high Defense that is counterbalanced by a low HP. 70 Speed allows it to reasonably outspeed most opponents.
Movepool: The only notable level-up moves Shellder learns are Clamp at level 23, which can slowly weaken an opponent, and Aurora Beam at level 30. Outside of those, Cloyster learns Surf and Ice Beam or Blizzard through TMs.
Major Battles: Beats Blaine, Giovanni, and Bruno easily with Water STAB, while Lance falls to Ice moves. With Clamp, Cloyster can slowly take out other opponents that can withstand special attacks easily.
Additional Comments: Shellder has a great typing, but levels up slowly and often comes underleveled. While players of Yellow can get it at level 40, those are rather uncommon, so they will need to spend some time fishing for it. Evolve with Water Stone either at level 23 after learning Clamp or at level 30 after learning Aurora Beam if you are not planning on teaching it an Ice TM.

Slowpoke (RB)

Availability: Mid-game (Route 23, level 23, caught as Slowbro) (Super Rod).
Typing: Water makes it useful against Blaine and Giovanni, while Psychic gives it a type advantage against Koga, Bruno, and Agatha.
Stats: Slowbro is a bulky Pokémon that is very slow and generally needs Amnesia boosts to hit hard with its 80 Special.
Movepool: Slowbro's offensive options are Surf, Psychic, and Ice Beam or Blizzard through TMs. Amnesia at level 44 allows it to sweep opponents that are not hit super effectively by its moves.
Major Battles: Slowbro handles Koga, Blaine, Giovanni, and Bruno with little trouble. With Psychic, it can also help against Agatha if it doesn't get crippled by status moves and can help against Lance with an Ice TM. Amnesia boosts allow it to contribute elsewhere.
Additional Comments: Slowbro comes underleveled and is hard to train due to its slow growth rate. It is also reliant on Amnesia boosts to OHKO a number of opponents and its low Speed lets it get worn out easily. Slowbro can also be caught at a higher level at Seafoam Islands with the help of Repels.

Farfetch'd (RB)

Availability: Early-game (trade a Spearow in a house in Vermillion City).
Typing: Normal / Flying gives it a good matchup against Erika and Bruno, but worsens the matchup against Lt. Surge and Lorelei.
Stats: Farfetch'd stats are rather low and do not hold it for long, though traded experience can help it outlevel opponents to compensate for that. Its Speed stat gives its Slash around 93% chance to land a critical hit.
Movepool: Farfetch'd greatly appreciates the Body Slam TM in order to hit hard immediately, with Fury Attack at level 15, Double-Edge through TMs, and Slash at level 39 being other alternatives. Swords Dance and Agility at levels 23 and 31 help it sweep, with the former combining well with all STAB moves bar Slash. Farfetch'd can also make a good HM slave, as it learns both Cut and Fly.
Major Battles: Farfetch'd generally needs to set up with Swords Dance and potentially Agility in order to sweep any team. This strategy is unreliable at the Pokémon League, as its low bulk makes it hard to set up consistently. Farfetch'd can also just pick off frail targets with Slash critical hits.
Additional Comments: Farfetch'd can make a great HM slave and also is easy to train due to traded experience. However, due to its low stats, it is forced to rely on setup against every major opponent and falls off at the Pokémon League anyways.

Farfetch'd (Y)

Availability: Mid-game (Route 11, level 26 or 31).
Typing: Normal / Flying gives it a good matchup against Erika, Koga, and Bruno, but worsens the matchup against Lorelei.
Stats: Farfetch'd stats are rather low and do not hold it for long, thus it has to rely on setup to compensate for them. Its Speed stat gives its Slash around 93% chance to land a critical hit.
Movepool: Farfetch'd greatly appreciates the Body Slam TM in order to hit hard immediately, with Fury Attack at level 15, Double-Edge through TMs, and Slash at level 39 being other alternatives. Swords Dance and Agility at levels 23 and 31 help it sweep, with the former combining well with all STAB moves bar Slash. Its only Flying-type option is Fly through HM.
Major Battles: Farfetch'd generally needs to set up with Swords Dance and potentially Agility in order to sweep any team. This strategy is unreliable at the Pokémon League, as its low bulk makes it hard to set up consistently. Farfetch'd can also just pick off frail targets with Slash critical hits.
Additional Comments: Farfetch'd has low stats and therefore is unable to perform well anywhere without having to set up. Furthermore, even with setup, it is an unreliable choice against the Elite Four, which further limits its usefulness.

Rattata

Availability: Early-game (Route 1, level 2-4).
Typing: Normal is useless against Brock and Agatha's Ghost-types and is weak to Bruno's Fighting moves, but is neutral elsewhere.
Stats: Rattata is a fast Pokémon, having a 18.95% chance of landing a critical hit, with a relatively fine 81 Attack stat. However, its stats fall off towards the later portions of the games and its bad Special prevents it from putting a good use to the many special TMs it learns
Movepool: Rattata's Tackle upgrades to Hyper Fang at level 14 and later Body Slam or Double-Edge through TMs. Super Fang at level 41 can be useful for weakening a difficult opponent. Raticate greatly appreciates Dig, as it gives it some good matchups in the late- and end-game, and also learns some special TMs like BubbleBeam, Water Gun, Thunderbolt, Ice Beam, and Thunderbolt.
Major Battles: Rattata performs well in the early-game, being able to sweep Lt. Surge and contribute against Brock with Tail Whip and Misty. After that, Raticate starts to drop in terms of viability and is generally limited to KOing frail threats like the Abra line, unless it's taught Dig, which allows it to perform well against RB Koga, Blaine, and Agatha.
Additional Comments: While Raticate starts off strong, it eventually falls off due to its unimpressive stats and is reliant on the Dig TM to maintain viability throughout the game. Furthermore, it is unable to use its wide TM learnset effectively due to its low Special.

Growlithe (R)

Availability: Mid-game (Route 7, level 18 or 20).
Typing: Fire, outside of giving it a type advantage against Erika, doesn't provide it with any inherent advantages. However, it doesn't give it any outright bad matchups either, outside of Lance, who resists it.
Stats: Arcanine's stats are all around good, most notably having a high Attack and being relatively fast.
Movepool: The line relies entirely on Ember and TMs, as the only useful level-up move Growlithe learns, Flamethrower, comes at level 50. Arcanine's best options from TMs are Body Slam, Double-Edge, Dig, and Fire Blast.
Major Battles: Arcanine performs the best if it knows Dig, as it can beat Koga, Blaine, and Agatha with it. It also performs well against Sabrina and its Fire Blast can easily pick off KOs at the Pokémon League.
Additional Comments: Growlithe's best performance is very reliant on the Dig TM and its viability drops significantly if it doesn't get it. Evolve with Fire Stone immediately, as waiting for Flamethrower at level 50 is not worth it.

Growlithe (Y)

Availability: Late-game (Pokémon Mansion, level 26, 30, 34, or 38 (first floor)).
Typing: Fire does not give Growlithe any advantages at this point of the game and makes it weak to Giovanni. It is also resisted by Lance.
Stats: Arcanine's stats are all around good, most notably having a high Attack and being relatively fast.
Movepool: The line relies entirely on Ember and TMs, as the only useful level-up move Growlithe learns, Flamethrower, comes at level 50. Arcanine's best options from TMs are Body Slam, Double-Edge, Dig, and Fire Blast.
Major Battles: Arcanine can perform well against Blaine and Agatha with Dig and also performs well against Sabrina. It can also pick off kills at the Elite Four with Fire Blast.
Additional Comments: Growlithe comes late and the only way for it to be any good is if you kept the Dig TM for that long to give it to Arcanine. Evolve with Fire Stone immediately, as waiting for Flamethrower at level 50 is not worth it.

Kangaskhan

Availability: Mid-game (Safari Zone (Central Area (east), level 25 (RB); Area 2, level 28 or 33 (Y));
Typing: Normal typing gives Kangaskhan a neutral matchup everywhere, bar against Agatha's Ghost-types and Bruno's Fighting-types.
Stats: Kangaskhan has a relatively good Attack and Speed, coupled with good Defense and HP. However, its Special is low, which repvents it from using its wide TM learnset effectively.
Movepool: Kangaskhan's best STAB move is Strength through HMs. Other useful TMs include Earthquake, Rock Slide, Seismic Toss, and Surf to handle Rock / Ground Pokémon. It also learns other special TMs like Ice Beam, Blizzard, Thunderbolt, and Fire Blast, though all have only situational uses.
Major Battles: Up until the Elite Four, Kangaskhan is able to reasonably OHKO or 2HKO most opponents that take neutral damage from its STABs, with physical coverage improving matchups when it hits super effectively. At the Pokémon League, it will generally OHKO or 2HKO Pokémon with super effective Rock Slide or Earthquake.
Additional Comments: Kangaskhan is a strong Pokémon that can learn many useful moves, but is hard to both find and catch. However, in Yellow, its encounter rate in Area 2 is slightly higher, being 15%.

Flareon

Availability: Mid-game (Celadon Mansion top floor as a level 25 Eevee).
Typing: Fire isn't really useful anywhere, outside of Yellow Koga, but doesn't grant it with outright bad matchups either.
Stats: Flareon's offensive stats are very high, with Flareon possessing one of the highest Attacks in the whole game. However, it is not very fast and it is not bulky physically.
Movepool: Flareon's movepool is rather poor, as it doesn't get many useful moves to take advantage of either of its offensive stats. Its physical options include Body Slam and Double-Edge through TMs, while special options include Fire Spin at level 36 (Y) or 44 (RB), Flamethrower at level 54 (RB) or 52 (Y), and Fire Blast through TMs.
Major Battles: Flareon is particularly good at KOing frail targets with a physical move, with bulkier threats being put in range with Fire Spin. Its Flamethrower and Fire Blast can also pick off KOs at the Pokémon League.
Additional Comments: Flareon has incredible offensive stats that are counterbalanced by a poor movepool and low Speed. Evolve with Fire Stone immediately, as Eevee doesn't learn anything useful by level.

Voltorb (RB)

Availability: Mid-game (Route 10, level 14, 16, or 17).
Typing: Electric gives Voltorb a better matchup against Lorelei and a neutral matchup everywhere else bar Erika and Giovanni.
Stats: Electrode is the fastest Pokémon in the entire game and has a 27.34% chance of landing a critical hit. Its other stats are not as high, unfortunately, with its Special reaching 80.
Movepool: The line is heavily reliant on the Thunderbolt TM for its best performance. Outside of that, it doesn't have much to go with, other than Selfdestruct and Explosion at levels 27 (as Voltorb) and 50 (as Electrode), though it generally has to weaken the target first to KO it, and support moves like Thunder Wave and Toxic through TMs.
Major Battles: Electrode performs well against Lorelei and Bruno's Fighting-types and can KO Lance's Gyarados and Aerodactyl. Outside of that, it can generally beat neutral targets that are not too bulky specially, though it is virtually useless against anything that resists Electric.
Additional Comments: Voltorb's biggest contribution is its great matchup against Lorelei. Although its offensive stats are not high, they are compensated by its high chance of landing a critical hit, allowing it to maintain viability against bulkier targets. You can also obtain it directly as an Electrode at level 43 at the Power Plant by picking up one of the fake item balls at the cost of a later arrival.

Voltorb (Y)

Availability: Late-game (Power Plant, level 43, caught as an Electrode from fake item balls).
Typing: Electric gives Voltorb a better matchup against Lorelei and a neutral matchup everywhere else bar Giovanni.
Stats: Electrode is the fastest Pokémon in the entire game and has a 27.34% chance of landing a critical hit. Its other stats are not as high, unfortunately, with its Special reaching 80.
Movepool: The line is heavily reliant on the Thunderbolt TM for its best performance. Outside of that, it doesn't have much to go with, other than Selfdestruct and later Explosion at level 50, though it generally has to weaken the target first to KO it, and support moves like Thunder Wave and Toxic through TMs.
Major Battles: Electrode performs well against Lorelei and Bruno's Fighting-types and can KO Lance's Gyarados and Aerodactyl. Outside of that, it can generally beat neutral targets that are not too bulky specially, though it is virtually useless against anything that resists Electric.
Additional Comments: Voltorb comes rather late and, due to its unimpressive Special, is not very useful for what is left of the game, though its high chance of landing a critical hit allows it to maintain some viability against bulkier threats.

Vulpix

Availability: Mid-game (Route 7, level 18 or 20 (B); buy at Rocket Game Corner for 1000 coins (Y)).
Typing: Outside of a type advantage against Erika and Yellow Koga, Fire typing doesn't give it any better matchups, with Lance also resisting it.
Stats: Ninetales is fast, having a 19.53% chance of landing a critical hit. It also has a great Special, but its other stats are lacking.
Movepool: Vulpix has to struggle with Ember until it learns Flamethrower at level 35. It also learns Confuse Ray at level 28. As a Ninetales, it appreciates the Dig TM to improve some matchups, while Fire Blast through TMs is a stronger Fire STAB move.
Major Battles: It struggles as a Vulpix against anything, though its performance improves a lot once it learns Flamethrower and evolves into Ninetales. With Flamethrower, it can perform well against any opponent that does not resist Fire, though specially bulky Pokémon like Alakazam and Gengar can avoid a 2HKO from it, with Dig giving it a better matchup against Blaine and Agatha.
Additional Comments: While Ninetales ia good Pokémon, you have to put up with the bad Vulpix period. While you could evolve it with a Fire Stone immediately, this would worsen Ninetales's performance in the long run, as it would have no reliable and powerful STAB move this way. You also have to spare the Dig TM for it so it can have some better matchups.

Moltres

Availability: End-game (Victory Road (2F), level 50, static encounter).
Typing: Fire / Flying provides it with a neutral matchup against whatever is left of the game.
Stats: Moltres has an incredibly high Special and the other stats aren't too bad either. However, they are held back by a lack of EVs.
Movepool: Moltres mainly uses Fire Blast and Sky Attack through TMs, with Fire Spin slowly weakning a bulky Pokémon.
Major Battles: Moltres can take on most Pokémon at the Pokémon League by hitting them with an appropriate STAB move. However, it will need Ethers and Elixirs to consistently take out more of them.
Additional Comments: While Moltres is very powerful, Moltres doesn't contribute much due to coming extremely late.

Electabuzz

Availability: Late-game (Power Plant, level 33 or 36).
Typing: Electric gives it a better matchup against Lorelei, although it's useless against Giovanni.
Stats: Outside of its 105 Speed, which gives it a 20.50% chance of landing a critical hit, its other stats are unimpressive, with its Attack and Special being 83 and 85.
Movepool: Although Electabuzz learns Thunderpunch at level 42, it is still better to give it the Thunderbolt TM, as it otherwise has to rely on Thundershock until then and because Thunderpunch misses on many KOs that Thunderbolt doesn't. Outside of those, Electabuzz can also be taught Psychic, Strength, and Submission through TMs for coverage.
Major Battles: Electabuzz is useful against Lorelei, Bruno, and Lance's Gyarados and Aerodactyl. Against the rest, it will generally do fine if the target is not specially bulky like Gengar or Alakazam, though the latter can be handled with Strength.
Additional Comments: Electabuzz comes rather late and is not powerful enough to be useful for what is left of the game, though its high chance of landing a critical hit can compensate for the unimpressive offensive stats.

Magmar

Availability: Late-game (Pokémon Mansion (3F), level 34) (B).
Typing: At this point of the game, Fire does not provide it with any inherent advantages and is even resisted by Lance.
Stats: Magmar's stats are largely unimpressive, with its 95 / 85 offenses not helping it for what is left of the game. However, it can outspeed most opponents reasonably with its 93 Speed.
Movepool: Magmar's Ember upgrades to Fire Punch at level 43, with Flamethrower coming at level 55 if you can reach that level. Fire Blast through TMs also provides more power, while Strength, Psychic, and Submission through TMs provide coverage.
Major Battles: Magmar generally doesn't sweep any of the remaining fights, though it can contribute to the end-game with a powerful Fire Blast and Sabrina with Strength.
Additional Comments: Magmar comes late and is not very useful for what is left of the game. Its only positive is that it learns a good Fire-type move by level.

Koffing

Availability: Late-game (Pokémon Mansion, level 30 (RB) or 32 (B)) (RB).
Typing: Poison is not useful for what is left of the game and gives it a weakness against Sabrina and Giovanni.
Stats: Weezing is rather slow, though it is rather bulky, particularly on the physical side. Its 85 Special allows it to hit hard only Pokémon with low special bulk.
Movepool: Koffing learns Sludge at level 32 and greatly appreciates Thunderbolt and Fire Blast through TMs. Selfdestruct and Explosion at levels 43 and 53 allow it to weaken difficult opponents later on.
Major Battles: Koffing performs well against Lorelei and Bruno's Fighting-types with Thunderbolt. Lance's Aerodactyl and Gyarados are handled by Thunderbolt, while his Dragon-types only use Agility or Barrier against it.
Additional Comments: Koffing comes late and is reliant on TMs to provide any usefulness for what is left of the game. You can also catch it directly as a Weezing with the help of Repels, though its level and rarity vary per game and floor. Note that Koffing is more common in Red than in Blue.

Grimer

Availability: Late-game (Pokémon Mansion (1F), level 30 (R), 30 or 34 (B) or 26, 29, 32, or 35 (Y)).
Typing: Poison is not useful for what is left of the game and gives it a weakness against Sabrina and Giovanni.
Stats: Muk has a high HP and Attack, though it's slow and its Special prevents it from using special TMs effectively.
Movepool: Grimer's only STAB move is Sludge at level 37. TM-wise, it can be taught Mega Drain, Thunderbolt, and Fire Blast.
Major Battles: Muk is able to take on physically frail targets with Sludge and on threats it can hit super effectively with TMs. In RB, it is useful against Lance, as his Dragon-types will always use Barrier or Agility against it.
Additional Comments: Grimer comes late and is not particularly useful for what is left of the game, being limited to KOing some Pokémon here and there. You can also catch it directly as a Muk at a higher level with the help of Repels, though its level and rarity vary per game and floor. Grimer is more common in Blue and Yellow than in Red.

Slowpoke (Y)

Availability: Late-game (Seafoam Islands (1F), level 28 or 30) (walking).
Typing: Water makes it useful against Blaine and Giovanni, while Psychic gives it a type advantage against Bruno, and Agatha.
Stats: Slowbro is a bulky Pokémon that is very slow and generally needs Amnesia boosts to hit hard with its 80 Special.
Movepool: Slowbro's offensive options are Surf, Psychic, and Ice Beam or Blizzard through TMs. Amnesia at level 44 allows it to sweep opponents that are not hit super effectively by its moves.
Major Battles: Slowbro handles Blaine, Giovanni, and Bruno with little trouble. With Psychic, it can also help against Agatha if it doesn't get crippled by status moves and can help against Lance with an Ice TM. Amnesia boosts allow it to contribute elsewhere.
Additional Comments: Slowpoke comes late and very underleveled and is hard to train, as it's very weak and levels up slowly. It also needs Amnesia boosts to perform well in many matchups. You can catch it as a Slowbro directly, but it's at 1% encounter rate and Repel tricking doesn't work here.

Psyduck (Y))

Availability: Late-game (Route 6, level 15 (Psyduck) or 15 or 20 (Golduck)) (Surfing).
Typing: Water allows Psyduck to perform well against Blaine and Giovanni, but doesn't provide it with any advantages elsewhere.
Stats: Golduck's stats are good, but not very high. The highest one is its 95 Special.
Movepool: Golduck is mainly relying on Surf and Ice Beam or Blizzard through TMs. It can be taught Dig and Seismic Toss through TMs for coverage.
Major Battles: Beats Blaine, Giovanni, and Bruno with no problems. With an Ice TM, it can handle Lance. It can also potentially contribute against Agatha if it knows Dig.
Additional Comments: Psyduck comes late and underleveled. Although it performs similarly to most Water-types in the game, the need to grind it to keep up with your team makes it inferior to the other Water-types in the game.

Ekans

Availability: Early-game (Route 4, level 6, 8, 10, or 12) (R).
Typing: Poison only gives it a resistance to Erika and a weakness to Sabrina. Arbok doesn't learn any useful STAB move, so it doesn't use it offensively.
Stats: Arbok's Attack and Speed are the only stats that are in any way impressive, though even those fall off later on, unless it is hitting super effectively. It is also fairly weak as Ekans.
Movepool: Ekans has to rely on Leer, Wrap, and Poison Sting until it learns Bite at level 17. Arbok also relies on the Dig or Earthquake TM (the former being preferred to make Ekans better earlier) to perform at its best. Other useful moves include Glare at level 27 and Mega Drain, Rock Slide, and Strength through TMs.
Major Battles: If it knows Dig (or Earthquake later on), it will perform well against Lt. Surge, Koga, Blaine, and Agatha. It also performs well against Giovanni with Mega Drain and Lance's Dragon-types, because they will always use Barrier or Agility against it and can also contribute against Lorelei with Rock Slide.
Additional Comments: Arbok is held back by its bad Ekans period, especially before it learns Bite. Furthermore, it's reliant on super effective hits to maintain viability later on, so its performance worsens greatly if it's not taught good TMs.

Hitmonchan

Availability: Mid-game (Fighting Dojo in Saffron City, Level 30).
Typing: Fighting type allows Hitmonlee to be useful against Lorelei, but is questionable against Sabrina and is not particularly useful for Koga and Agatha.
Stats: Hitmonchan has a good Attack, but its Speed is not very high and its bulk, especially on the special side, is very bad.
Movepool: Hitmonchan's most optimal moveset comes from TMs. Its only STAB move is Submission, with Strength acting as coverage and Toxic being a support move. Hitmonchan also learns Fire Punch, Ice Punch, and Thunderpunch at levels 33, 38, and 43, but its low Special prevents it from using them effectively.
Major Battles: Hitmonchan struggles to sweep any fight outside of the first one against Giovanni. It generally contributes by OHKOing frail targets with STAB Submission, though it's also useful against Lorelei.
Additional Comments: Hitmonchan struggles to perform well against most fights due to its bad bulk and poor movepool. Its only positive traits are that it comes at a high level, its usefulness against Lorelei, and its ability to OHKO some Pokémon easily.

Pidgey

Availability: Early-game (Route 1, level 2-5 (RB) or 2-4 (Y)).
Typing: Normal / Flying gives it a good matchup against Erika, Yellow Koga, and Bruno's Fighting-types. However, it is bad against Brock, Lt. Surge, and Lorelei, as well as against any Rock-type Pokémon.
Stats: Pidgey and Pidgeotto's stats are not very good and are stuck with them for long due to Pidgeotto's late evolution. Only after it evolves into Pidgeot do the stats become acceptable, though they fall off later on anyways.
Movepool: Pidgey's Gust and Quick Attack upgrade to Double-Edge through TMs. For a Flying-type move, it can use Fly through HM and later Sky Attack through TMs. It can also be taught support TMs like Reflect and Toxic, as the line doesn't get anything else that is useful.
Major Battles: The line beats Erika, Yellow Koga, and Bruno's Fighting-types just with a Flying STAB move. Outside of those, the line generally contributes by KOing frail opponents with STAB moves, though it can also OHKO some threats at the Pokémon League with Sky Attack.
Additional Comments: Despite coming early, Pidgey is limited in its contributions due to its lackluster stats, typing, and movepool. You can also catch it directly as a Pidgeotto in Yellow's Viridian Forest, but it's at 1% encounter rate, so it's not worth it.

Pinsir

Availability: Mid-game (buy at Rocket Game Corner for 2500 (B) or 6500 (Y) coins; Safari Zone (Central Area (hub)) at level 23 (B) or Area 3 at level 25 (Y)).
Typing: Bug is useless for Pinsir offensively, as it learns no Bug-type moves. Defensively, it gives it a weakness to RB Koga and Blaine and a resistance to Giovanni and Bruno's Fighting-types. Its Speed also makes its Slash a guaranteed critical hit.
Stats: Pinsir has one of the highest Attack stats, along with a good Defense and Speed, though its other stats are bad.
Movepool: Pinsir's only viable offensive moves are Strength and Submission through TMs and Slash at level 49. It can combine Strength and Submission with Swords Dance through TMs to sweep opponents. In Yellow, it also learns Bind at level 21.
Major Battles: Pinsir generally performs well by setting up Swords Dance and then using an appropriate move. This strategy is ineffective against Agatha's Ghost-types, though Pinsir can damage them with Seismic Toss.
Additional Comments: Pinsir's shallow movepool forces it to rely on setup to sweep any fight. Furthermore, it levels up slowly and is a hassle to obtain, regardless of the game and your preferred method.

Ponyta

Availability: Late-game (Pokémon Mansion, level 28, 30, 32, or 34) (RB); Mid-game (Route 17, level 28, 30, or 32) (Y).
Typing: Fire only gives Ponyta an advantage against Erika and Koga in Yellow, while in RB, it doesn't provide it with any good matchups.
Stats: Rapidash is fast and has a good Attack, along with an okay Special, though its other stats are bad.
Movepool: Ponyta's STAB options are Ember, Fire Spin at level 39, and Fire Blast through TMs. Outside of that, its only forms of coverage are Body Slam and Double-Edge through TMs.
Major Battles: In Yellow, it can contribute against Erika with Ember and Koga with Fire Spin. In both games, it is useful against Sabrina and is generally good for KOing frail targets or hitting opponents hard with Fire Blast later on.
Additional Comments: Ponyta is held back greatly by its useless typing and shallow movepool. While it comes earlier in Yellow, it doesn't perform well enough to distinguish itself from its Red and Blue variant tier-wise.

Scyther

Availability: Mid-game (buy at Rocket Game Corner for 5500 (R) or 6500 (Y) coins; Safari Zone (Central Area (hub)) at level 23 (B) or Area 2 at level 25 (Y)).
Typing: Useless offensively, as Scyther learns only one STAB move that is unhelpful. Defensively, it gives it an advantage against Erika, Giovanni, and Bruno's Fighting-types and a weakness to Koga and Blaine.
Stats: Scyther is fast and always lands critical hits with Slash. It also has high stats, though it's not very bulky.
Movepool: Scyther's most optimal movepool consists of Slash at level 29, Double-Edge through TMs, and Swords Dance at level 35. In Yellow, it also learns Wing Attack at level 50.
Major Battles: Scyther only performs well by setting up Swords Dance and then using Double-Edge, though it will have to heal sometimes due to recoil. It can also pick off frial targets with Slash, though it's useless against Agatha, unless it knows Wing Attack.
Additional Comments: Scyther has a shallow movepool, levels up slowly, and is a hassle to get, no matter which method you go for.

Venonat

Availability: Mid-game (Safari Zone (Area 2), level 32, caught as Venomoth) (RB); Early-game (Route 24, level 13 or 16) (Y).
Typing: Bug / Poison gives it a type advantage against Erika and RB Koga, while resisting Bruno's Fighting-type moves. However, it leaves with a weakness to Sabrina and Blaine, though it also hits the former super effectively.
Stats: It is very weak as Venonat and Venomoth's stats are not very high either, with its highest being 90 Special and Speed.
Movepool: In Yellow. Venonat has to manage with Tackle, Confusion at level 11, and Leech Life at level 27 until it evolves. It can also be taught Psychic and Mega Drain through the TMs, with Psybeam at level 38 being an alternative for the former. Sleep Powder allows it to cripple an opponent that Venomoth would struggle against otherwise.
Major Battles: Venomoth is good for Erika with Leech Life, while Koga and Bruno are defeated with Psybeam or Psychic. It can also contribute against Giovanni with Mega Drain. The other opponents generally have to be put to sleep, as they can take its attacks easily and wear it down in return.
Additional Comments: Venomoth is not very powerful and relies on sleep in order to beat anything that it doesn't hit super effectively. While Venonat comes earlier in Yellow, its inability to be useful for the earlier fights counterbalances the earlier arrival.

 

[DHR-107]

Doing a quick QC here as DSG asked me too.

S Rank

Abra: Odd question, Is Kadabra just as S worthy as Alakazam? Like, the difference between the two is negligible?
Clefairy: Probably remove the second "Many" under movepool (to target weaknesses).
Jynx: Honestly surprised its in S when you have to sequence break hard to get it early. The context works, but who would even use Jynx vs Blaine?
Mr Mime: Typo for confusion under movepool. Maybe reword the Major Battles section as it reads odd to me
Nidoran-F: You use "performance" a whole bunch of times here. Maybe try swapping one of them out and see how it reads.
Nidoran-M: Same as above. If they are this similar, isn't it just worth talking about them at the same time if they are in the same tier and there isn't any realistically huge differences between them?


A Rank
Articuno: Major Battles; Odd sentence when you list Blaine and Lorelei? I think its missing a comma or something. Under Additional Comments "However, its biggest flaws is" should probably be "biggest flaws are". Also you could just finish that sentence with "Seafoam islands being out of the way" to avoid repeating Obtain again.
Jigglypuff: Reading this entry makes me wonder why its in A Rank at all. Heavy TM usage and a reliance on Sing doesn't sound like an A Rank mon to me? Sure it can take a hit, but it sounds like it needs a lot of help. If you're determined to keep it in A, I would reword this slightly more positively.
Sandshrew: You mention basically all the gym leaders under typing, then repeat it later on under major battles. Probably move the information about Gym Leaders to just Major battles and tweak the Typing section.

B Rank
Bellsprout: Typing has merged into Availability here
Geodude: Im confused why you are mentioning Self Destruct and Explosion here? No one will ever use them.
Jigglypuff Y: Again, considering how harsh the A Rank is for Jiggly for RB, can we not merge these?
Machamp: Probably explain where the trade Machoke is located?
Seel: Formatting issue; Major Battles merges into Movepool
Spearow: Formatting issue; Movepool merges into Stats

C Rank
Krabby: Typing; issue with grammar "Water make Krabby"
Shellder: Why are we mentioning Self Destruct and Explosion?
Vulpix: Formatting issues

D Rank
Caterpie: Only briefly mentioning its matchup vs Brock is a bit of an odd one, considering its one of the few mons that can easily play around bide and still come out reasonably well.
Dratini: Its probably worth mentioning Agility alongside TWave for the same Wrap strategies
Ekans: Not mentioning RB Koga here under typing is odd when you mention Erika. Also formatting issue at the end.
Electabuzz: Formatting issues.
Growlithe: Formatting issues.
Lickitung: mfw it doesn't learn Lick in Gen 1
Ponyta: Formatting issues
Scyther: Odd sentence structure under typing? I get what you mean but not how its written.
Tangela: Formatting issues. Tangela is also available directly south of Pallet town in RB for a non trade version.

E Rank
All fine

Just a quick-ish glance through everything here. Let me know if you need anything explained.

 

[Ryota Mitarai]

Drums is a bit busy so he asked me to address some things on his behalf

Abra: Odd question, Is Kadabra just as S worthy as Alakazam? Like, the difference between the two is negligible?

If I have to keep it short, it's because it's a fast and hard-hitting Special that learns Psychic by level. Requires no contested TMs to do well and Lance is the only matchup where it's truly bad. Yes, Alakazam is better, but Kadabra on its own is still excellent and worthy of S. You could try searching in the main thread if you need more details

Nidoran-F: You use "performance" a whole bunch of times here. Maybe try swapping one of them out and see how it reads.
Nidoran-M: Same as above. If they are this similar, isn't it just worth talking about them at the same time if they are in the same tier and there isn't any realistically huge differences between them?

well, the thing is, they are different Pokemon, no matter how you look at them, because the base Pokemon are with different Pokedex numbers. I personally don't think merging two Pokemon with different base dex numbers in one is a good idea, since there are other Pokemon that are virtually the same (with minimal differences) that you could argue should be merged this way (not necessarily in this game).

Jynx: Honestly surprised its in S when you have to sequence break hard to get it early. The context works, but who would even use Jynx vs Blaine?

This was a bit of a hot topic in the main thread. I am going to let Drums answer this, as he argued for S on it the most.

Jigglypuff: Reading this entry makes me wonder why its in A Rank at all. Heavy TM usage and a reliance on Sing doesn't sound like an A Rank mon to me? Sure it can take a hit, but it sounds like it needs a lot of help. If you're determined to keep it in A, I would reword this slightly more positively.

Fwiw I have never really supported strongly A either (at best I suggested that it's not necessarily impossible for it to be A, but I have always leaned towards B myself), someone else campaigned for this placement. I asked Drums about this and he's happy to drop this and merge it with the Yellow one.

Machamp: Probably explain where the trade Machoke is located?

It already is? Unless you meant to be more detailed, because the Availability section does refer to the traded one

Tangela is also available directly south of Pallet town in RB for a non trade version.

We deliberately ommitted that one, because we were aiming to list the most optimal availabilities rather than every single one. While Dratini has two availabilities itself, it's cause we felt both were equally (un)optimal to be included.

As for Explosion/Self-destruct, they are mentioned where they are mentioned, because the mons that use it don't really have much else to use (other than alternative (weaker) STABs). They allow them to KO some threats like Alakazam (bar Golem, which uses it to KO some aces instead, like Erika's Vileplume). Also, in this gen (and I believe up to gen 3), successful Explosion or Self-destruct that outspeeds the opponent cancels their turn, so it's essentially free damage and free pivoting for most parts.

tl;dr they are mentioned mostly cause the stuff don't really have much else to run and because they can have some use (like KOing key threats or giving you free turns)

grammar and formatting errors will possibly be corrected tomorrow, per Drums's words. Feel free to respond to any of my comments

 

[Xator_Nova]

Regarding Jigglypuff, this is a bit theorymonning since I haven't used it like I used Clefairy in tests, but given that both of them have the same Attack and similar availability, Jigglypuff and Clefairy should inflict similar damage with Mega Punch and Mega Kick, so Jigglypuff shouldn't really need the special TMs until the Elite Four. The Jigglypuff analysis doesn't reflect this, so perhaps that could be added to make its position in A Tier more convincing in case it's still desired to preserve Jigglypuff in A (it doesn't seem to be the case though)

 

[DrumstickGaming]

Jynx: Honestly surprised its in S when you have to sequence break hard to get it early. The context works, but who would even use Jynx vs Blaine?

Jynx is late, yes, but it is exceptionally broken. Trade EXP, incredible STAB combo, sleep access allows it to cheese things it shouldn’t like Blaine (and you can get to his last mon there fairly easy IIRC, if not sweep). Also sweeps the ENTIRE E4.

Sequence breaking isn’t really a factor in its ranking imo. If you don’t have it for Erika, it’s not that bad. Jynx COULD BE A, but it’s just so tough it rips through the second half of the game with absolute ease. All you need to do is TM it Psychic (not an issue IMO) and it tears everything up, and the 2% of things it doesn’t it has Lovely Kiss for. Heck, you could even TM BubbleBeam on if you really hate Blaine.

So yes, Jynx is for sure an S. Kadabra is also an S, you don’t need Zam for it to bend the game over its spoon.