Cloyster

Cloyster's unique access to Spikes, Shell Smash, Skill Link, and Icicle Spear allows it to act as a potentially fearsome wallbreaker or sweeper that can bypass Substitute and Sturdy as well as pressuring rival entry hazard setters such as Nidoqueen and Rhyperior while being able to set up hazards itself. Thanks to its enormous Defense and use of Focus Sash, Cloyster is almost guaranteed to set up either Shell Smash or one layer of Spikes. While those attributes sound incredibly appealing in RU's more offensive metagame, keep in mind that Cloyster lacks coverage to hit common Steel-types such as Registeel, Metagross, and Bronzong super effectively. Cloyster's Defense is amazing, but its Special Defense combined with its relatively low unboosted Speed usually leaves it threatened out by Pokemon like Roserade, Raikou, Gardevoir, and Mega Sceptile prior to boosting. Its bad defensive typing also leaves it vulnerable to all entry hazards, especially Stealth Rock, and Fighting-types like Machamp, Toxicroak, and Bewear. It also has to be cautious of Taunt from Pokemon such as Mandibuzz, Houndoom, and Vanilluxe, which stops it from setting up Spikes or boosting with Shell Smash, making it much less dangerous. Cloyster is also shut down by status conditions, cutting its sweep short. Even if Cloyster does set up, it is easily shut down by priority moves such as Bullet Punch from Machamp and Accelerock from Lycanroc-D. Cloyster faces a lot of competition for a spot on a team. As a physically offensive Water-type, it has to compete against Barbaracle and Golisopod because both of them have a stronger offensive presence before boosting and are better at pressuring Steel-types. As a Spikes setter, Roserade and Golisopod are arguably more appealing because Roserade is faster, applies immediate offensive pressure without having to set up, and has all the tools it needs to pressure entry hazard removers, while Cloyster usually has to resort to Explosion, and Golisopod does not have Cloyster's Fighting weakness, can pressure Steel-types with Liquidation, has priority in Aqua Jet and First Impression, and can pivot with Emergency Exit.