Shellder

Shellder (Japanese: シェルダー Sherudaa) is a -type Pokémon introduced in Generation I.

Physiology
Shellder is protected by its two large shells. Its large tongue is always kept hanging out. It has two large eyes inside the shell.

Natural abilities
Shellder can have the ability Shell Armor or the ability Skill Link. Shell Armor prevents Shellder's opponents from getting a critical hit on Shellder. Skill Link increases the frequency of multi-hitting attacks. As a last resort, Shellder clamps on to its opponents. It swims backward by opening and closing its two shells.

It is said (in the anime & in-game Pokédex entries) that if a Shellder clamps onto a Slowpoke's tail the Slowpoke will evolve into Slowbro (the Shellder changes shape with it). Also if a Shellder clamps on Slowpoke's head the Slowpoke will evolve into a Slowking. According to Slowking's Pokédex entries, when the Slowpoke's head is bitten, toxins enter the Slowpoke's head (and into its brain), unlocking extraordinary power and triggering evolution. These same toxins also causes a Slowbro to no longer be able to feel pain.

According to Slowbro's & Slowking Pokédex entries, the Shellder's produce toxins that affect either their victims brain (in Slowking's case) or their nervous system (in Slowbro's case). It is also said that if a Slowbro's or Slowking's Shellder is removed or detached it (Slowbro/Slowking) will revert (devolve) back to a regular Slowpoke.

Also it is said that Shellder's tend to latch on to a Slowpoke if it is holding a King's Rock (a reference to Slowking's requirements for evolving).

Upon the Slowpoke's evolution the Shellder changes it form into either Slowbro's shell (attached to Slowbro's tail) or a Slowking's crown. In its crown form the Shellder eyes are located on it backside (which can be easily seen by the player character when a Slowking is used in battle), basically giving Slowking eyes in the back of its head.

Evolution
Shellder evolves into Cloyster by use of a Water Stone.

Leveling
Generation VI=

Generation V=

Generation IV=

Generation III=

Generation II=

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Generation I=

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Anime

 * Marilyn's Shellder