Onix is a Rock Snake Pokémon. Its serpentine body is made up of large boulders and little pebbles. It has a long horn atop its head and small eyes.
Onix can have the abilities Rock Head or Sturdy. Rock Head prevents Onix from recoiling, while Sturdy gives Onix immunity to OHKO moves . When it is burrowing underground, it can cause rumbles and earthquakes. It can dig at speeds up to 50 MPH. It has a compass in its brain that can tell Onix what direction it is facing.
Brock received an Onix from his father, Flint, on his 10th birthday, as seen in a flashback in Having a Wailord of a Time . Onix was Brock's 1stPokémon and has consistently been his most powerful Pokemon as well.
The Crystal Onix's first and only appearance is in the anime episode The Crystal Onix. Ash and his friends first heard of it through a note they found in a bottle floating in the ocean. The note was written by a little girl named Marissa. She wanted to find the Crystal Onix to help her brother, Mateo, gain inspiration to make glass Pokémon statues. Mateo told a story of how his grandfather discovered the Crystal Onix and then was able to make extraordinary sculptures afterwards. One of those sculptures included the Crystal Onix itself.
Unshō Ishizuka, the actor best known for playing Professor Oak in the original Japanese version of the anime voices both Onix and its evolved form, Steelix in both the Japanese and English-language versions of the anime.
Before the second generation of Pokémon came about, Onix was the largest Pokémon of them all.
Its name comes from "Onyx," a black stone that is commonly used in jewelery.