Shellder

Shellder is a Water-type Pokémon that dwells on the ocean floor. It is marked as No. 090 in the National Pokédex.

Pokédex Data
Shellder, known as the Bivalve Pokémon, is an ocean-dwelling mollusc with a black pearl-like body concealed within a violet-coloured bivalve shell. It has wide, white eyes and constantly-extended pink tongue. Shellder uses its tongue to burrow into the sand on the ocean floor and also uses it as a lure to capture prey. The tongue is always extended, even when Shellder's shell is closed. Pulling on Shellder's tongue will cause its shell to pop open.

Shellder shares a symbiotic relationship with the Dopey Pokémon, Slowpoke. By clamping onto Slowpoke's tail, Shellder triggers Slowpoke's evolution into Slowbro and becomes permanently bonded to it, taking on a spiraled cone shape with several tiers. In this form, Shellder continously injects a toxin into Slowbro's blood that renders it incapable of feeling pain and amplifies its psychic abilities. Shellder may also trigger Slowpoke's alternate evolution into Slowking by clamping onto the head of a Slowpoke holding a King's Rock, becoming Slowking's crown.

Abilities

 * Clamp - Shellder's signature move. Its shell closes and bites into the opponent with tremendous pressure, inflicting damage over a steady period.
 * Withdraw - Shellder closes its shell to protect itself from attacks.
 * Water Gun - Shellder spews a stream of water at enemies to inflict moderate damage.
 * Icicle Spear - Shellder produces a series of sharp icicles that whittle away the opponent's HP.

Evolution
Shellder triggers the evolution of Slowpoke into Slowbro, or Slowking if Slowpoke is holding a King's Rock. In Galar, Shellders are attracted to Slowpokes wearing Galarica-based accessories; it can cause a Slowpoke to evolve into Slowbro by biting the arm of one wearing a Galarica Cuff or trigger a Slowking evolution by biting down on a Slowpoke's head that's wearing a Galarica Wreath.

Shellder may also evolve on its own when exposed to a Water Stone, becoming Cloyster.