Onix basically resembles a giant chain of gray boulders, with a rocky spine on its head. The Pokémon has a magnet in its brain that serves as an internal compass. Onix's body becomes more rounded and smoother as it grows with age. A fully grown Onix measures at an enormous 28 feet 10 inches, or 8.8 meters.
They are very hot headed Pokémon and will constantly attack humans and Pokémon when various objects are caught in its craggy body. However, domesticated Onix will show signs of distress instead of attacking others.
Onix's Sturdy works like a Focus Sash, causing Onix to have 1 HP remaining if an attack's hit would have brought it from full health to 0 HP. This ability can be used again if the user is brought back to full HP.
Multi-hit, swipe moves can break through Sturdy, like the Focus Sash. When a swipe move hits a Pokémon with Sturdy, Sturdy's effect activates for only the move's first hit, not the entire move.