Quoted By:
I raised an Alola-Muk on my Ultra Sun team, and she was incredibly useful and kicked a lot of ass. Granted, it helped because I bred Shadow Sneak and Curse on her.
But regular Muk is fine, too. Muk is one of those Pokémon I never considered training as a kid because Psychic-types were so overpowered and Poison-types were their bitches. Maybe this prejudice is the reason that Poison-types don't typically get a lot of love. Thankfully, Psychic-types aren't that powerful anymore, so Poison-types could experience a renaissance like Bug-types did in Gen 5.
