Cloyster has a large shell covered in spikes. Six of the spikes are long and conical, resembling turrets, and are used to protect its soft insides from foes. However, the shell offers a lack of protection against special attacks. Cloyster has an inner, gray-colored layer inside its purple shell. Its "head" and face resemble a black pearl, and there is a jutting, horn-like white spike above its "head". Its face is similar to Gastly, though the two Pokémon are not related.
Gender differences
None.
Special abilities
Cloyster possesses incredible defensive capabilities unrivaled anywhere else in the Kanto region. Cloyster’s entire fighting style is focused around its uncanny defense: its shell. Cloyster attacks by firing sharp spikes off of its shell while it is kept tightly clamped shut. It is said to be impossible to open from the outside. Aside from its remarkable defense, Cloyster is also capable of unleashing a considerable arsenal of offenses, mostly including Water and Ice-type attacks, but reaching to Poison and Dark-type as well. While this Pokémon is generally unmoving on land, though capable of moving quickly only underwater using jet propulsion, has been recorded as having the ability to inexplicably float through the air.
Behavior
In spite of its grim semblance and its menacing guise, Cloyster's behavior is actually quite unremarkable. In battle, the cowardly Cloyster clamps its monstrous, impenetrable shell tightly shut so that it may not be forced ajar. It then attacks recklessly and aimlessly in all directions with the random, ballistic fire of the spikes on its shell. This haphazard, hit-or-miss style of attack does not earn Cloyster high respect in the field of tactical gumption or cleverness. Though its personality may be lacking, the grimace on its face is perpetual.
Ash battled a Cloyster belonging to Pete Pebbleman during the Indigo League in Fire and Ice. It reappeared in a flashback in Friends to the End. Also, in the latter episode, another Cloyster under the ownership of an unknown Trainer, appeared during the closing ceremonies of the Indigo League.
First seen against Yellow in conjunction with her Dewgong. Later, in the battle on Cerise Island, it kept the voodoo dolls of Green and Sabrina (which kept their arms bound by an ice cuff) safely out of reach while Lorelei battled them. Although it initially seemed that with Green out cold, Sabrina stood little chance, she feigned attacking repeatedly and slowly sapped Cloyster's strength using Mega Drain, eventually fainting it. Lorelei realized this, and quickly took back the dolls.
Cloyster reappeared again in Lorelei's attempt to defend Seven Island. It is then remarked that Cloyster is the strongest fighter Lorelei has in her arsenal due to the tough shell it possesses, said to withstand the damage of a Napalm Bomb. However, though they fought valiantly and pushed Sird to her limits, ultimately the insidious villain won by having her Starmiecamouflage itself and attack where they couldn't defend.
The boss of Team Rocket, Giovanni, is shown in several rounds using Cloyster. He used it to freeze two Magmar after having a chat with Red. Then, when Red came to beat him, he used it to freeze Poli.
In the Pokémon Adventures manga, Cloyster is drawn by Mato as having a blue marking like a jewel on its head, beneath the spike. The official art by Ken Sugimori, however, does not. This is likely because the white circle seen on Cloyster's head in most early sprites and the Generation I Sugimori art was interpreted by Mato as a jewel, but was actually intended just to be glare. Satoshi Yamamoto, who took over starting at Volume 10, did not make the same error.
Pokémon Pinball: A Cloyster appears on the Blue Table. When the pinball can be shot into the Cloyster, Catch'em Mode is activated, allowing for the capture of a Pokémon.
Pokédex entries
This Pokémon was unavailable prior to Generation I.
Cloyster is capable of swimming in the sea. It does so by swallowing water, then jetting it out toward the rear. This Pokémon shoots spikes from its shell using the same system.