While I don't like a lot of the Alolan Pokemon, and especially their legendaries, I do like some of the alternative Alolan Forms that they introduced.
Marowak:Godddamn did this guy get an upgrade. He went from trash tier to omega tier. Not only is his typing superb in fire / ghost, but he still gets lightning rod. Lightning rod is an incredible ability, especially in multi battles.
Then he still gets to use his unique item, thick club, which doubles his attack to an unbelievable number. He also has a bunch of his old unique moves but since he isn't ground type any more, they aren't STAB. He does however get a new one called shadow bone (lol). Also he gets flare blitz as STAB now. Goddamn.
That being said, he's really slow. And he will die, it's not like he's invincible or anything. He's just way better than what he used to be.
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Muk:I really like this variant of Muk. In fact, I prefer it a lot more to its normal version. The typing is way better, removing the huge weakness to psychic completely. It's still weak to earthquake, but nothing you can do about that.
Also it now has way better STABs. Having dark type means it can do way more with knock off or pursuit, giving it way more offensive ability whereas in the past it mostly had to rely on gunk shot. Now it's a major threat to so many more things, as opposed to just stuff weak to poison. This guy can easily manhandle most psychic and ghost types, among many other things.
It's still really tanky and hurts way more now. What's not to love?
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Ninetales:This guy is strong as fuuuuuck. Not because it does a lot of damage. It actually doesn't really do that much damage at all with a really crappy special attack stat.
It's because of the skill aurora veil, which is basically reflect and light screen combined into one. During hail. Which it just so happens, Ninetails summons every time it enters battle.
Granted, it's kinda crap if you can disrupt the weather yourself but goddamn it's annoying if you can't.
Other than that it's pretty worthless though. I mean, it can still nasty plot itself but the base special attack is really bad. It'll take at least two plots for it to become more than a hassle. It's relatively survivable though... for an ice type.