Yadoking

Slowking is a bipedal Pokémon with a Shellder latched onto its head. It is primarily pink, with a pale yellow muzzle and scaled belly. Its feet and hands each have a single clawed digit, while the hands also have a clawless thumb. Around its neck is a spiny ruff with alternating red and white stripes. The Shellder on its head has a spiral shape with two horns near the base. A red gem resides in the center of the Shellder.

Shellder's bite releases venom into Slowpoke's brain, causing a chemical chain-reaction that unlocks a superior intelligence and extraordinary power. More venom is injected into Slowking every time it yawns. The more venom the Shellder releases, the more intelligent Slowking will become. However, if the Shellder on its head comes off, it will forget everything it has learned. Slowking's intelligence can match that of a human and it constantly attempts to learn more. Its inspiration and intuition are also highly developed, and Slowking is able to stay calm in any situation and plan situations with effective results.

(Source: Bulbapedia)