There is more to this shady clam than what meets the eye. Cloyster's stat spread might scream ''physical wall'', but that's hardly the case, for it gets access to arguably the best boosting move in the game: Shell Smash. After just a turn of setup, Cloyster turns into a wrecking ball that can mow through entire teams with ease. With Skill Link, Cloyster can also abuse a powerful STAB Icicle Spear, which has an enormous 187 BP after STAB, as well as a great coverage move in Rock Blast; this ensures that even Substitute users cannot stop Cloyster's rampage. A massive base 180 Defense makes Cloyster all the more difficult to revenge kill, as it can comfortably survive powerful priority moves such as Mach Punch from the likes of Breloom and Conkeldurr even after a Shell Smash. Unfortunately, Cloyster's horrendous Special Defense means it simply can't take a special attack to save its life, and a weakness to Stealth Rock makes switching in even more difficult. It also finds it difficult to get past bulky Water-types such as Jellicent, which can take Cloyster's boosted attacks with ease and burn it, rendering it useless. Underestimating Cloyster on the basis of these shortcomings will be suicidal, though; it can run through your team like a hot knife through butter.
It is not hard to see why this is Cloyster's most threatening set. With its immense physical bulk, Cloyster can easily set up a Shell Smash on physical attackers such as Dugtrio, doubling its Attack, Special Attack, and Speed in one fell swoop; after a Shell Smash, Cloyster will sit at a frightening 578 Attack, 412 Special Attack, and 524 Speed with the given EV spread. It can then go to town with its powerful STAB Icicle Spear, which has an enormous 187 Base Power with STAB and Skill Link. Additionally, this ensures that Cloyster will be able to KO most threats through Substitute and Multiscale. Rock Blast is Cloyster's main coverage option, dealing heavy damage to the Fire- and Water-types that resist Icicle Spear.
Hydro Pump is the preferred option in the last moveslot, as it destroys bulky Steel-types such as Skarmory, Scizor, and Forretress looking to soak up a boosted Icicle Spear. However, Razor Shell can be used to OHKO Tyranitar and Heatran, which can survive a boosted Hydro Pump with a specially defensive EV spread and OHKO in return. The choice between the two depends on the support which Cloyster's teammates can provide: if these two Pokemon are handled easily by your team, then running Hydro Pump is better.Team Options & Additional Comments >>>
While Cloyster does have access to Shell Smash, don't forget that it also has a massive base 180 Defense, allowing it to counter top physical threats such as Garchomp and Excadrill. This set works best as a bulky attacker on offensive teams needing a solid answer to the aforementioned threats, but it fits equally well on stall teams which can provide Cloyster with the support to take powerful special attacks. Cloyster can also set up entry hazards and provide Rapid Spin support to its teammates; its function is thus similar to that of Forretress, the difference being its greater offensive presence.
Icicle Spear allows Cloyster to act as a solid check to Dragon-types such as Dragonite; it also ensures that Substitute users such as Gliscor and Mienshao will not be able to set up on it. Cloyster's poor Speed and dreadful Special Defense might make Rapid Spin appear to be a bad choice, but it can easily pull off a Rapid Spin against Pokemon such as Skarmory, which cannot deal much damage to it. Spikes and Toxic Spikes are both options for the third slot: the choice between these two depends on the entry hazard which Cloyster's teammates cannot set up. Hydro Pump is the preferred option for the fourth moveslot, providing coverage on the Fire- and Steel-types which resist Icicle Spear; it OHKOes Excadrill and Chandelure and deals heavy damage to physical tanks such as Skarmory.Team Options & Additional Comments >>>
Ice Shard can be used on the Shell Smash set to beat priority users such as Breloom to the punch; it also deals heavy damage to the few threats which outspeed Cloyster, such as Choice Scarf Latios. Toxic is an option on the utility set to cripple bulky Water-types such as Jellicent. Spike Cannon could be used to give Cloyster Water / Normal coverage, but Rock Blast provides better coverage overall. King's Rock, while it appears gimmicky, actually gives Icicle Spear and Rock Blast a 41% flinch chance, meaning Cloyster can get past bulky checks such as Jellicent with a lucky flinch. Finally, Explosion might seem usable on the utility set to go down with a bang, but the nerf which it received in BW makes it pretty much unusable.
Checks and Counters
Few threats outspeed Cloyster after a Shell Smash, meaning priority is one of the best answers to it. If Cloyster takes Stealth Rock damage, Breloom and Conkeldurr can OHKO it with Mach Punch, and Choice Band Scizor can 2HKO with Bullet Punch while surviving even a boosted Hydro Pump at full health. Having Stealth Rock on the field is thus a basic step to keeping Cloyster in check. Alternatively, Vacuum Wave users such as Infernape and Lucario make great checks to Cloyster as they target its weak Special Defense. A fast Choice Scarf user such as Latios can outspeed Cloyster even after a Shell Smash and OHKO it. Imposter Ditto in particular can switch in after Cloyster sets up and use the Shell Smash boosts to its advantage, pulling off a sweep of its own.
There also exist several Pokemon which can sponge Cloyster's boosted attacks and OHKO in return. Jellicent is only 2HKOed by a boosted Rock Blast and can cripple Cloyster with Will-O-Wisp. In the same vein, Vaporeon and Slowbro don't take much damage from a boosted Rock Blast and can KO back with the appropriate move. Jirachi is barely 2HKOed by a boosted Icicle Spear, and can paralyze Cloyster or OHKO with Thunderbolt. Ferrothorn can take a boosted Icicle Spear from sets lacking Life Orb or Icicle Plate, and can deal heavy damage with Power Whip or cripple Cloyster with Thunder Wave. Skarmory, while it can't do much damage with Brave Bird, can Whirlwind Cloyster out and end its sweep. Lastly, Unaware Quagsire ignores Cloyster's Shell Smash boosts and can set up with Curse, taking out Cloyster after a few Curse boosts while healing off any damage taken with Recover; however, it needs to be careful while switching in as Icicle Spear can 2HKO with a high damage roll.