I'll have my opinions on the Pokemon I used fairly often in my playthrough:
Rowlet
Even though it mostly spent the game getting experience from the Exp. Share (mostly involuntary from my part, I admit), it did its part well.
IMO, Physical Rowlet is the best way to go because most of the good special TMs are post-game only, whereas you can eventually get moves like Swords Dance (why isn't Nasty Plot a TM, now that I wonder?), Sucker Punch and Spirit Shackle before completing Ula'Ula. It tends to lack room for Roost, however.
I think it takes a hit during that bad movepool drought between getting Razor Leaf and Pluck and getting Leaf Blade and Brave Bird (they come really late) so you may end up relying on non-STAB attacks until, at least, it gets Spirit Shackle.
Likely not the best starter to pick, though, given Popplio and Litten get better STAB combinations. Rowlet can still pull its weight, though.
Pikipek
Early-game Brick Break availability is a godsend, both for patching up the usual questionable early bird coverage (I mean, it only gets Bullet Seed when it becomes a Toucannon) and being much better than Rock Smash, which it may have got by the time you get the Brick Break TM.
Other than that... it does not really have anything special. It lacks a good Normal-type level-up move (the best it can get is Skill Link Fury Attack, which is weaker than Bullet Seed despite STAB) and it only learns Brave Bird as an egg move, but Beak Blast can compensate, being a reliable 100 BP STAB move, Toucannon being slow enough the low damage phase priority does not matter much, and helping burn clear threats that have contact moves.
Its usability drops down drastically after evolving into Toucannon, but it's not because Toucannon is slow and not that bulky... but rather because the Pikipek and Trumbeak phases are really good in comparison, getting good moves quickly, having access to some nice early-game TMs, evolving fast and hitting fairly hard at that spot. It starts like, say, an improved DPP Starly, but in the end it's not like DPP Staraptor. This also extends to match-ups - in Moon, Trumbeak OHKOes the Totem Raticate, while it also easily breaks through Hala and the Totem Lurantis, whereas after evolving into Toucannon, it gets no advantages in match-ups, and even struggles in the second match vs Hala, doing little more than spreading burns with Beak Blast... and for that, one would rather run Talonflame with Will-O-Wisp.
Wingull
While I boxed my Drizzle Pelipper after getting a Jangmo-o (this being my intention all along; Pelipper was a filler), I'll gladly tell anyone against such a decision.
After a very short rough start (the Trainers' School's Teacher's Magnemite, I mean), Wingull starts getting more and more cool toys to play with. The turning point is getting Scald, Roost and the Waterium Z and evolving into Pelipper, where it gets from 'alright' to 'OMG'. With those three things, Drizzle Pelipper gets through a lot of things with rain-boosted Scalds or Hydro Vortexes, whereas it gets an impressive only two bad match-ups in Hau's Raichu (which is still difficult to deal with for most Pokemon IMO) and the Totem Vikavolt.
It only gets cooler once it gets Hurricane (quite late, however) and U-Turn to deal some chip damage before switching out.
There really isn't much to say other than it's Hydration->Drizzle or nothing. It's a very straightforward Pokemon - click on a STAB, and watch things drop.
Oricorio (Pom-Pom)
I believe the viability of this specific Oricorio sort of depends on the Hidden Power type you get, since it gets practically nothing outside of Revelation Dance and Flying-type moves. Mine's Hidden Power was Grass-types, awfully convenient given Flying/Electric coverage's most common stops are weak to Grass.
It's a fairly ok mon anyways. Early Air Cutter is great, then it starts to disappoint until it shoots back with Air Slash and Revelation Dance, and then you get the unreliable yet powerful Hurricane.
You can also pull Baton Pass thanks to it being able to learn Work Up, but I think it doesn't have the room for both moves - late-game, at least.
Cubone
Alolan Marowak is the living example of a disappointment. Which is a shame, not because of its cool design or actual competitive uses, but because it starts fairly well as a Cubone. If you bother to get a Thick Club for it, you get a powerful physical attacker until it's time for it to evolve - which is generally late enough for it to OHKO the Totem Salazzle with Bonemerang.
But after it evolves... the inexplicable decision of having Alolan Marowak's signature move, Shadow Bone, be only learnable through the Move Relearner is absolutely terrible. Alolan Marowak is stuck with
no STAB moves other than Flame Charge until it reaches Level
53 (Flare Blitz) you reach the top of Mount Lanakila...
home of the Elite Four. Yeah, that late. It is also stuck with generally weak or inaccurate coverage moves in Rock Tomb or Bonemerang until late-game.
This mean it does not hit as remotely hard as you'd want it to hit even when factoring on the Thick Club boost. I admit, Lightning Rod Marowak can wall entire types on its own, and it makes the battles against Guzma look like a joke, but it does not pull much elsewhere until you can give it good STAB moves... where the game is almost over.
Salandit
Salazzle is another disappointment to me, but for a different set of reasons. It's not her rarity (A male Cute Charm Sylveon is fairly easy to get, and Eevees with a Fairy-type move are available a few routes before you first find wild Salandit), but rather because she does not deliver what she seems to deliver.
Salazzle has a nice STAB combination, solid offensive stats and access to Nasty Plot, but... she often falls short of OHKOes with her STABs, and her serious frailty means she almost never gets the chance to Nasty Plot against relevant opponents. A drought of coverage moves means Salazzle is deadweight against pretty much anything that is not weak to her STABs.
And talking about moves... she's stuck with Flame Burst for about twenty levels (and I may not be exaggerating) and her poison STAB move is even worse - you either have to rely on a Toxic+Venoshock combo, or wait until almost Level 40 to get Sludge Bomb.
In the end, I used her only against Pokemon weak to her STABs, or as a revenge killer. Salazzle's useless outside of that.
Jangmo-o
Fine, I understand that lore states that Jangmo-o's line is only found in mountains... but Alola has a lot of mountains - why is Jangmo-o a rare very late game encounter? I mean, Mount Hokulani could have been a good place for them to start showing up...
This means a few things:
- Jangmo-o is obtained when all its good match-ups have passed. You only have the Totem Kommo-o, the second Lusamine battle and the Elite Four to fight, and it can only really pull its weight against Lusamine (not against Clefable, of course) and the Totem Kommo-o (only if Soundproof, and you'll have to grind a lot if you want to use it for that battle).
- By the time you get it, Jangmo-o is only two-five levels away from evolving into Kommo-o. This does not really matter much for usefulness, but it's more of the complaint about it being a late-game rare Pokemon.
Kommo-o's good stats, fine movepool (although Dragon Dance is a late level-up move, so you are stuck with Swords Dance) and three abilities that provide immunities are mostly wasted by being too late to showcase them.
