Snorlax

Behold, the single most dominant Pokemon in any OU tier in history. Snorlax combines power and resilience with deadly unpredictability, a set of traits that lands it a spot on virtually all serious teams. Its presence defines the GSC metagame, all but forcing teams to play one or more sturdy Normal-resistant Pokemon while simultaneously killing off the viability of manifold special attackers with its enormous HP and sky-high Special Defense. Snorlax is a constant threat to offensive teams as a Curse sweeper, a team-sweeping machine as a Belly Drum user, a relentless battering ram as a mixed attacker, and a reliable wall as a RestTalk user. However, it isn't completely unstoppable. Snorlax's Defense stat is on the low side, meaning that despite its massive HP stat, Explosion from common OU Pokemon like Cloyster and Exeggutor is enough to take it out with minimal prior damage. It will usually be forced to use Rest if it gets poisoned, giving the opposing team a reprieve that they can use to gain an advantage. Defensive teams will nearly always have Skarmory for Snorlax and usually pair it with a semi-reliable counter to mixed Snorlax as well, which can sometimes leave Snorlax unable to do any meaningful damage by itself. However, make no mistake: these constitute but minor flaws among Snorlax's array of overwhelmingly powerful attributes.