Rattata

From the Pokémon Encyclopedia

Rattata is a small, but unspecialized rodent. Its most notable feature is its large teeth. Like most rodents their teeth grow continuously throughout its life, and must be constantly worn down by gnawing. It will bite anything when it attacks; yet it will live peacefully side by side with Pidgey. Small and very quick, it is a common sight in many places. It has long whiskers and a long, slightly curled tail. Rattata has purple fur on its back, and cream colored fur on its stomach. This coloration, called countershading (dark on top, light on bottom), is a common protective mechanism for many small animals.

A newly-caught Rattata knows Tackle and Tailwhip. It has the Guts and Run Away abilities; its other moves may include Bite, Quick Attack, Reversal, and Super Fang. It evolves into Raticate at level 20.