Snorlax

Snorlax is a centerpiece of the RBY OU metagame. It is present on almost every team due to its incredible strength, bulk, and versatility, in spite of its terrible Speed. Thanks to Reflect, Snorlax can upgrade its physical bulk to truly remarkable levels and begin firing powerful Body Slams with little concern about incoming hits. Defensive answers to its Body Slam do exist, but Snorlax has access to a plethora of options to threaten them, such as Earthquake to get around Gengar and Counter users, or Ice Beam to freeze Pokemon which try to fight Snorlax's Reflect with their own. Furthermore, Snorlax can even opt to give up a traditional Reflect set and catch opponents off-guard by using less common moves such as Amnesia or Counter, which can allow it to bypass some common answers, and it even has access to the strongest Self-Destruct in the game, giving it the ability to eliminate almost any Pokemon if necessary, with only Gengar and Rhydon being able to comfortably absorb it.

Despite all these positive qualities, Snorlax comes with two inherent flaws: the lowest Speed in the metagame, only tied with Slowbro, and a lack of recovery outside of Rest. This means that once Snorlax is put to sleep it is possible for many special attackers in the tier to threaten it with their STAB moves: Psychic from the likes of Exeggutor, Starmie, Alakazam, and even Jynx can rapidly snowball out of control due to the high chance of Special drops, and other strong attacks such as STAB Thunderbolt from Zapdos or STAB Blizzard from any of the Ice-types in the tier can also ensure Snorlax is punished for its Rest turns. Nevertheless, Snorlax is one of the biggest offensive threats and one of the hardest Pokemon to KO at the same time, and its set can be tailored to cover any desirable match ups effectively, which means it's usually hard to find reasons not to run Snorlax on your team.