Snorlax

With its high bulk, strong Attack, and expansive movepool, Snorlax is one of the tier's most effective offensive and defensive Pokemon. Curse Snorlax is one of the most difficult Pokemon to check around, being difficult to KO, offensively threatening, and able to customize its set to defeat its potential counters. Defensively, Snorlax is one of the most important checks to Latios and Latias, and it soft checks a variety of other threats including Mewtwo, Deoxys-A, Jirachi, and Regice. Snorlax is also a highly effective wallbreaker, capable of forcing trades with Curse or with STAB Self-Destruct, which is stronger than every Explosion. Immunity and Thick Fat are both useful abilities on an already good defensive Pokemon, blocking one of the most prevalent ways of stalling Snorlax out or making it a highly effective Ice- and Fire-type sponge. However, Snorlax's unboosted physical bulk is not great, and many Pokemon run Fighting-type moves almost exclusively to take advantage of it. Snorlax is also very slow and has no options to rectify this weakness beyond spreading paralysis, meaning that once it is at low health, it is effectively KOed.