This Onix is a rock/ground-type Pokémon owned by Brock.
Onix, along with Geodude, was used by Brock in his battle against Ash. They were defeated by Ash's Pikachu, Fearow and Caterpie.
Onix was used to battle against Haunter along with other Pokémon and attempted to bind it by wrapping itself around it, but was defeated when Haunter used Dream Eater.
None of Onix's moves are known.