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Onwile's large horn mimics Onix, scaring away Pokémon that would normally predate the smaller core body. It lures in prey by acting injured and having the horn act like inanimate rocks, before lunging and devouring the target with the large maw.

Its giant jaws are actually steel horns that transformed. There is a magnet in its brain that prevents an Onwile from losing direction while tunneling.