I am not very experienced in the specifics of Pokemon and Damage Calculation. So I cannot do much in the way of that. But ever since my beloved Gengar was refused Gengarite and is forced to contend with Ubers, I want to put my say in when it comes to my equally loved Mommy Kanga.
I would like to point out a few things that will hopefully defend Momma right now.
You probably already know some of the info I will recount, but I encourage you to read it anyway just so I feel like it was worth my time and if I made a mistake you can correct me. ^.^
Typing
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1.) Mega Kanga is stuck on Normal Typing.
The only plus is that its immune to ghost and takes less damage from Stealth Rocks. Besides that it has a half resistance to Steel and Rock. Rock only having as far as I know one viable move because of its higher crit chance and Steel only having Bullet Punch which is just a weak priority. (Which is why Fariy's are a bit of a problem right now.) Besides that Normal takes a 2x weakness to the common offensive type Fighting. With the variety of powerful normal effectiveness moves that could OHKO Kanga, you would have to play her very cautiously.
Meaning that it's only stab moves are normal moves.
Normal Moves Kanga can use. Besides that Normal is a pretty bad type to have.
Comet Punch: Not a huge threat when it comes to competitive because of how luck based it is. If for some reason you come across this. If Kanga somehow hits 5 times in a row it will do 135, and the baby would only hit once for 13.5 pwr (not sure if pokemon rounds down or up).
1 Hit 27
2 Hit 54
3 Hit 81
4 Hit 108
It would need to hit at least 3-4 times to be useful and the odds are hardly with you.
Fake Out: An okay opening move that flinches the opponent. Good for predicting a switch and messing up a set up while at the same time damaging your opponent. This can screw Sash Sweepers and a variety of other sets. The problem lies in its damage.
60 Pwr with STAB accounted for. Plus Kanga wouldn't even be able to use the benefit of the scary Power Up Punch to aid it because this only gains its Flinch Potential the first turn Kanga is out. Making it one of the less powerful moves in her arsenal. This move is strong, but Kanga could use this before and was always low-tier. The second hit from the baby will add half of the dmg. Meaning that this priority move is more of a threat, but the fact that it only works once unless your opponent switches and the main concern appears to be 'power up punch for the win lol' means that he wont be doing that much.
Double Hit: 52.5 with stab. 90 accuracy .Guaranteed to hit twice (when it hits) with half damage from one of the hits coming from the baby.
Yeah this move is good. Yeah its another sash breaker. Which is something I would like to point out.
This Pokemon is a GREAT sash breaker, and having a good sash counter that isn't rocks feels fresh, which makes me want to defend it more.
But yeah... this move is a bit hard to defend. Besides the fact that normal offensively doesn't do any bonus damage to anything and does nothing to the increasing ghost threat.
Rage: 30 pwr with stab on first attack, with the baby doing 15pwr
In a competitive scene where switching out and team balance is key,rage will not fare very well anywhere, especially here.
Mega Punch: 120 Pwr 85 accuracy.
Sweet Damage, will hurt if it hits, but deemed unreliable a lot. (because it is)
Dizzy Punch 105 with stab.
This is a pretty dangerous move. 40% chance to confuse with good damage. This is one of those moves that make your really consider how strong Kangaskhan is... until you remember that confusion goes away when you switch out. The damage is nice, but when it confuses... it wont have that much impact.
Chip Away 105 with stab
Ignores defensive boosting abilities. Would be good if anyone used defense boosting moves in ou. You may as well use Dizzy Punch.
Endure: ???pwr (Not sure if it accounts for Stab)
An... interesting move where if you can predict your opponent was not predicting you to switch would be a really good move. Also, typical physical sweep couldnt use this.
Hyper Beam: 225 with stab second hit would do half of that. 90% acc
HOLY SHIT DAMAGE!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
I would try to bullshit you and say that the 90% acc justifies this, but it doesn't.
The only downside is that Sp. Atk Kanga holds no weight. But still, I had to point this out.
(This makes me question why Normal Sp.Atk sweepers aren't popular. With how often you have to switch the lost move wouldn't matter on most occasions.)
Return 153 with stab with max friendship
EVERYBODY GET ON BOARD THE U.S.S. FRIENDSHIP, CAUSE IF YOU AREN'T ON IT, YOU WILL GET WRECKED.
Honestly, this is one of the big threats, and what makes Kanga competitive in OU. This is what makes her a good physical sweeper that can compete with the rest, and allows us to appreciate the return of the momma! Yet, this can be countered by a ghost type or someone physically defensive.
Other Threats I have seen that don't have stab.
Power Up Punch 40 pwr
It's a new move that is probably only really viable on Kangaskhan because of the fact that she gain the boost from this move twice. Giving her a swords dance that deals damage. Which is pretty nifty and unique.
Unfortunately, she doesn't gain stab.
A thing to note however is that Kanga gains the boost from each punch individually, giving the baby a boost in damage, meaning it will deal 75% of the damage of the first punch (i think).
Bite 60 power 30% chance to flinch
With the double hit this is a 60% chance to flinch.
This is really good and makes Kanga an even better Utility Sweeper.
Earthquake 100pwr
Okay, I get it. Strong non-stab type coverage that does tons of damage... this is sometimes a problem unless your opponent is flying. Also pretty good to catch your opponent off guard when they think they got you countered.
That's all the moves I could think of or find that seemed note-worthy
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Stats
Since Mega Evolution has max priority then I wont even bother mentioning base Kangaskhan's stats.
HP 105 Pretty average. Nice for a bulky physical sweeper, which is how I typically build Kanga because of its lack of resistances.
Attack 125 A nice upgrade but compared to most sweepers it's just average.
Defense 100 Pretty nice bonus. Kanga is a pretty balance stat bar line.
Sp.Atk 60 Another reason why Sp. Atk Kanga would never be a problem.
Sp.Def 100 Again, a nice flat bonus.
Spd 100 Not going to out speed anyone that stats into it. Might as well build bulky.
Building Kanga as a tank won't really get you anywhere. Like I mentioned Kanga has a great utility movepool made stronger by the second hit. Yet the highest chance disable like move you have is bite, and that is still 60%. Having mediocre and balanced defenses are both good and bad. You won't be a strong Def or Sp Def but you could be a balanced hp meat sack. Yet after taking note you would be wasting the bonus of the attack the strongest role that there is is the attack aspect. Which is really strong.
Yet I don't think its strong enough to warrant basically a ban in ubers, where she wouldn't last a second.
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In short.
If you keep Kanga in OU you have an above average sweeper that will do fine if its counter isn't out. Yet if anyone has a fair team balance they can easily catch Kanga in a sweep, or block her. Since her kit would be heavily based on Fighting and Normal, she is screwed when a ghost enters the picture. Just because Mega-Gengar is out doesn't ruin the competitiveness of Gengar, the new threat Aegislash, and other ghost threats like Mega-Bannete.
If you put Kanga in ubers because of its fast power boosting, you put this Pokemon in a position where it probably wouldn't last against a lot of the threats floating around in ubers. Kanga does not have the power to last there and just because of a reaction to one cheep combo that doesn't warrant starving Kanga in ubers.
Kanga has already gone a long way up the tier list, yet lets stop this train at OU.
I have to the best of my ability tried to defend Kanga. I'm not the most intelligent Pokemon player but I am giving my opinions with the knowledge I know to try and defend Kanga. Cause Gengar was put in Ubers and I felt bad not having a say in it. Hopefully this isn't too painful to read and my hour or so work on this post wont be in vain.