Cloyster

Cloyster holds a niche in Ubers thanks to its combination of unique traits; it has fantastic physical bulk, letting it tank Snorlax's Self-Destruct, Mew's +2 Earthquake, and Tauros's Hyper Beam with relative comfort. Its Ice typing gives it a powerful STAB Blizzard as well as an immunity to freeze. It also has access to the mighty Explosion, a potent tool in Ubers, and its signature move Clamp can choke down slower foes and provide free switches for its teammates.

However, Cloyster is weighed down by multiple detrimental traits that prevent it from being a true oppressive force in Ubers. Its matchup into unparalyzed Mewtwo is horrendous, only 5HKOing it with Blizzard while being 2HKOed by Psychic and Thunderbolt in return, letting Mewtwo switch in with little risk. It can't reliably switch into the physical attackers it wants to tank hits from, as it becomes much worse if it is paralyzed by Body Slam or Thunder Wave. Cloyster also finds it difficult to heal off the damage it takes, as its only way of healing is Rest, which forces it into complete passivity for two turns. Cloyster also relies on heavy paralysis support to effectively use Clamp and Explosion due to its mediocre Speed and weakness to special moves.