Moves
Shell Smash is a must on Cloyster, boosting its offenses to dangerous levels and allowing it to sweep unprepared teams at a moment's notice. Icicle Spear is Cloyster's most powerful and reliable STAB attack, which is guaranteed to hit five times due to Skill Link, reaching 125 Base Power. This lets it easily break through Focus Sash and Substitute, as well as OHKO Intimidate users such as Salamence and Landorus-T even at -1. Rock Blast is another move that benefits from Skill Link and offers Cloyster coverage against Fire- and Ice-types such as Charizard, Volcarona, Glalie, and opposing Cloyster, while also hitting bulky Water-types that resist Icicle Spear neutrally, such as Rotom-W, Suicune, and Slowbro. These attacks are non-contact moves as well, meaning that common Rocky Helmet users such as Cresselia and Hippowdon cannot hurt Cloyster with residual damage outside of Toxic and, in Hippowdon's case, Sand Stream. Ice Shard is a STAB priority move that is very useful because Cloyster struggles to take a hit after Shell Smash's defense drops. It also helps against other priority users such as Thundurus, Talonflame, and Breloom. Alternatively, Razor Shell gives Cloyster a secondary STAB option that it can use to OHKO defensive Heatran and Mamoswine after a Shell Smash boost.
Set Details
An Adamant nature along with full investment in Attack gives Cloyster maximum damage output. Cloyster is relatively flexible with the amount of Speed investment it can run; 140 EVs allow it to outspeed all the relevant threats up to Adamant Choice Scarf Landorus-T after a Shell Smash boost. However, 100 Speed EVs can be run if only outspeeding the base 135 Speed tier is desirable, or even 84 EVs if you only need it to outspeed Mega Gengar. The rest of the EVs go into HP, Defense, and Special Defense to increase Cloyster's overall bulk. A much simpler spread of 252 Atk / 4 Def / 252 Spe is viable if you want Cloyster to outspeed every +1 base 100 Speed Pokemon after one Shell Smash boost; this includes common Dragon Dance users such as Mega Charizard X and Speed Boost Mega Blaziken. It also allows Cloyster to Speed tie with Adamant Breloom prior to Shell Smash. A Jolly nature with maximum Speed allows Cloyster after a Shell Smash to outspeed everything up to the base 110 Speed tier at +1, including Choice Scarf Latios, while Speed tying with maximum Speed Breloom before the boost. King's Rock is the best item on Cloyster, pairing nicely with Skill Link and Cloyster's multi-hit moves to provide a great 41% chance to make the foe flinch. Cloyster can fully take advantage of King's Rock to potentially muscle through defensive threats such as Rotom-W, Cresselia, Porygon2, and Mega Venusaur. Focus Sash means Cloyster can always survive a hit, allowing it to set up on special attackers such as Gengar and Thundurus, which would otherwise OHKO it with their STAB move of choice; however, this is normally outclassed by King's Rock's ability to immobilize slower and bulkier threats. Lum Berry is an option to allow Cloyster to set up more effectively, as it wouldn't be fearing Breloom's Spore, Hippowdon's Yawn, or Thundurus's Thunder Wave. Skill Link is chosen to guarantee Icicle Spear and Rock Blast hit five times.
Usage Tips
Cloyster has a large enough presence at Team Preview that your opponent will think twice before sending out their physical attackers and common Ground-type leads such as Garchomp and Landorus-T, and even going up against these threats usually means a chance to boost. Therefore, you can use Team Preview to your advantage when picking your lead. With that said, Cloyster is best used as a lead, especially if it runs Focus Sash. Don't be careless by switching into Outrage and Earthquake, as both of these moves have a high chance to 2HKO it. Go for an early Shell Smash take out as many threats as possible or simply try to make them flinch before going down, and then let your team clean up. It's better to leave Cloyster for later or bench it entirely if you're against teams that have Steel- and Water-types, particularly Mega Mawile, Aegislash, Suicune, Rotom-W, and Slowbro, or against rain offense or Trick Room teams. You can afford to be more aggressive if running Substitute or Lum Berry, as it allows Cloyster to use Shell Smash much more safely against moves such as Hippowdon's Yawn, Breloom's Spore, and Suicune's Scald.
Team Options
Volcarona is able to easily threaten out the Steel-types that Cloyster struggles with, such as Aegislash and Mega Mawile, while Cloyster eliminates Ground-types such as Garchomp, Landorus-T, and Hippowdon, all of which threaten Volcarona. Dual screen setters such as Klefki and Raikou are particularly helpful to Cloyster, making it extremely difficult to take down. Assault Vest Raikou can also help Cloyster by sponging nasty Electric-type attacks such as Thunder Wave and Thunderbolt, and in return Cloyster can set up on the Ground-types that Raikou doesn't like. Thunder Wave support from Thundurus is also appreciated for Cloyster due to its low Speed prior to Shell Smash. Consider Mega Charizard X when using Cloyster, as Mega Charizard X appreciates the removal of Ground- and Dragon-types, which Cloyster can set up on. Mega Gengar is great for trapping defensive walls that Cloyster might have trouble breaking through, such as Slowbro and Cresselia. Bulky Ground-types such as Landorus-T and Hippowdon help Cloyster deal with Steel-types such as Aegislash and Mega Mawile. Chansey can come in on any special attacker that may threaten Cloyster, such as Thundurus, Greninja, or Mega Charizard Y, and provide Thunder Wave support if required. Talonflame threatens Fighting-types such as Breloom and Blaziken and is able to burn Mamoswine with Will-O-Wisp. Specially defensive variants of Talonflame can also deal with Aegislash, which can easily wall Cloyster, very well. In return, Cloyster can help Talonflame remove Ground-types that it struggles with, such as Garchomp and Landorus-T. It can set up Shell Smash against these threats, as they would most likely want to get up Stealth Rock as soon as possible upon seeing both Cloyster and Talonflame in Team Preview. Heatran can take special attacks relatively well and beat Steel-types for Cloyster, while Cloyster can take Earthquake thanks to his high natural physical bulk and remove Ground-types for Heatran. Serperior can easily set up on and remove bulky Water-types such as Suicune, Rotom-W, and Slowbro and is able to spread paralysis through Glare or set up dual screens to allow Cloyster to boost more easily. Cresselia has access to Lunar Dance and other support moves such as Thunder Wave and Toxic, and it can also easily wall bulky attackers such as Mega Kangaskhan and Conkeldurr.
