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Deals damage and has a 30% chance to flinch the target.
Headbutt is too weak to be useful on most Pokemon. Many Pokemon can attempt to use it for the flinch chance, but it is far too weak to be recommended for competitive use when there are so many better options available.
Body Slam is a more powerful alternative which boasts a 30% paralyze chance.
Double-Edge is much stronger, but cannot flinch the opponent, and has recoil damage.