With the introduction of BW, Cloyster received a gift it could only have dreamed of: Shell Smash. With one of the best boosting moves around, the clam now finds itself being able to perform an entirely different role as one of the most threatening sweepers around. Taking Cloyster's Skill Link ability into account, it can abuse a 125 Base Power Icicle Spear and Rock Blast at +2 Attack, which will destroy anything that doesn't resist them. Its Water-type move of choice also makes sure that Steel-types aren't surefire counters, as a +2 STAB Hydro Pump or Razor Shell will inflict huge damage to most of them.
However, Cloyster isn't without its flaws. Its Ice typing provides it with a crippling weakness to Stealth Rock, as well as often-seen priority moves such as Mach Punch. With Conkeldurr and Lucario in the tier, one has to make sure they are eliminated first or Cloyster won't be able to sweep after setting up. Cloyster also has some troubles getting past bulky Water-types, such as Jellicent and Vaporeon, that can burn or phaze it and thus prevent a sweep.
Cloyster's main set is one that can sweep most teams with ease; in fact, it's a liability to have a bulky Ground-type when your opponent has a Cloyster. This set is best used on an offensive team, where other sweepers can open up holes in defensive cores for Cloyster to take advantage of. Shell Smash doubles Cloyster's Attack, Special Attack, and Speed to threatening levels. Icicle Spear is the perfect move for Cloyster; because of Skill Link, it will always hit five times, effectively making it a 125 Base Power STAB move. Rock Blast offers great coverage with Icicle Spear, hitting Fire-, Water-, and Ice-types for at least neutral damage. In the last slot, you may choose among its alternative Water-type STAB moves and priority. After a Shell Smash, Razor Shell OHKOs Tyranitar and Heatran without rain and Scizor with rain; all of these KOs require Stealth Rock support. Razor Shell also inflicts the most damage to specially defensive Jirachi, and it can even wear down physically bulky opponents with its 50% chance to lower their Defense by one stage. Hydro Pump is the preferred option for getting past Skarmory, Forretress, and non-specially bulky Scizor since it hits their weaker Special Defense; however, it loses out on taking out specially bulky Tyranitar and Heatran with Stealth Rock support. Either STAB move is crucial for hitting certain Ice resists, mainly Steel-types and Mamoswine, after a Shell Smash boost. One may opt for Ice Shard, though, to prevent Scarf Latios or Breloom from revenge killing Cloyster, as well as providing a strong priority check against Landorus, Landorus-T, Tornadus, Thundurus-T, and Dragon-types.Team Options & Additional Comments >>>
While Cloyster is normally used as a Shell Smash sweeper, it has a unique niche defensively. This set focuses on its base 180 Defense and utility moves in a way similar to Forretress; in exchange for a less useful defensive typing, you gain a significantly better attacking capability. STAB Icicle Spear takes out threats such as Dragonite, Substitute Gliscor, and Sturdy Level 1 Aron.
Icicle Spear remains the biggest selling point of Cloyster, since it receives a STAB boost and will always hit five times thanks to Skill Link. Rapid Spin may seem like an ineffective choice when Cloyster is both affected by all entry hazards and is weak to Stealth Rock, but it often finds opportunities to spin hazards away against physical tanks and many physical attackers on offensive teams. Spikes or Toxic Spikes should be used to soften up the opponents team or when a bulky Ghost-type switches in, but using both on the same set is inadvisable; Cloyster fills its niche more effectively with another attacking move and will certainly not have the opportunity to set up both hazards. Surf is a good secondary STAB move to broaden coverage against Steel-types, Fire-types, and Mamoswine, but Ice Shard is also useful to pick up a possible KO on Gengar and to revenge kill threats such as Dragon-types and Landorus.Team Options & Additional Comments >>>
Explosion could see use on one of Cloyster's sets, but with the mechanics change in BW, it is much less effective and thus better off not being used. Toxic could also get some use on the utility set to wear down bulky Water-types, but due to its poor Special Defense, Cloyster will take large damage even from their resisted attacks, leaving it unable to effectively stall them out. Also, a Choice Scarf set can come in handy for checking faster threats such as Dragonite, Landorus, Virizion, Tornadus, Latios, and Infernape, among others. However, it is generally not recommended, as Cloyster's lack of power is usually its downfall without Shell Smash to boost its stats.
Checks and Counters
Being part Ice-type is a double-edged sword for Cloyster. On one hand, it gains an awesome STAB move, on the other, it takes 25% damage from Stealth Rock whenever it switches in, and is liable to being hit by both Spikes and Toxic Spikes. For this reason, having Stealth Rock on the field is a good first answer to Cloyster. A Bullet Punch from Choice Band Scizor will 2HKO Cloyster after it has taken Stealth Rock damage, while the only thing Cloyster can do back is Hydro Pump, which fails to OHKO Scizor even at +2, leaving aside the fact that it has shaky accuracy; if rain is up however, Scizor will be easily OHKOed. Mach Punch users are also Cloyster's worst enemies; Life Orb Adamant Breloom has a fairly high chance to OHKO without Shell Smash's defense drop after Stealth Rock damage, while unboosted Conkeldurr follows closely with a 2HKO. As Cloyster is incredibly fast after Shell Smash, there aren't many Choice Scarf users that can outspeed it after it gets a boost. However, Latios can do so and will send the clam sinking back to the briny depths with Draco Meteor. Under the sun, Chlorophyll users, such as Venusaur and Sawsbuck, can be customized to be faster than a +2 Cloyster, as well.
Generally speaking, bulky Water-types and Steel-types can handle Cloyster. Bulky Rotom-W resists Cloyster's STAB moves, and isn't too fussed about Rock Blast. It can promptly OHKO the clam with Thunderbolt, making it a good switch-in to Cloyster in general. Jellicent and Tentacruel also have the capability to annoy Cloyster greatly. Both can use Scald on Cloyster and hope for a burn, as well as other options that can put a damper on Cloyster's life; Will-O-Wisp from Jellicent will help prevent Cloyster from being a huge problem, and Tentacruel's option is Toxic, which will quickly wear Cloyster down when used in tandem with Protect. Slowbro is another bulky Water-type who can tank anything that Cloyster can throw at it, and target its weaker Special Defense stat with Psychic or Flamethrower; it can also use Thunder Wave on Cloyster to cripple it for the rest of the game. Keldeo deserves a special mention for being an offensive Water-type that survives +2 Cloyster's offensive artillery with plenty of health to spare.
Skarmory can't do much to Cloyster, but can Whirlwind it out to prevent the immediate problem. This is significant due to the fact that Cloyster usually carries a White Herb, and Cloyster is extremely vulnerable later on in the game without this precious item. Defensive Jirachi can quite easily take Cloyster's Water STAB move, and retaliate with Thunderbolt on a Calm Mind version or Body Slam and Iron Head on a physical version. Ferrothorn can take a +2 Icicle Spear, and either hit back with Power Whip or cripple Cloyster with Thunder Wave. Thanks to Unaware ignoring Shell Smash boosts, Quagsire can take Icicle Spear nicely and Toxic Cloyster back, or even hope to burn it with Scald. A slightly unusual but effective option to deal with Cloyster is specially defensive Heatran; if Hydro Pump is favored over Razor Shell on Cloyster, it will be unable to OHKO Heatran even at +2. In return, Heatran will OHKO Cloyster after it's taken Stealth Rock damage with Lava Plume. Take note that if rain is up, Heatran will be destroyed by any Water-type move from Cloyster.