Onix

Onix is a rare Rock, Ground-type Pokémon from Kanto region. It evolves into Steelix when fed with 50 candies and Metal Coat is used.

Pokédex description
Rock Snake Pokémon

''Onix has a magnet in its brain. It acts as a compass so that this Pokémon does not lose direction while it is tunneling. As it grows older, its body becomes increasingly rounder and smoother.''

Evolution family
Onix is the part of a two-member family.