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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. Dunsparce, with Serene Grace, can abuse Headbutt's flinch chance along with paralysis from Glare. 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.
Return is stronger, but cannot flinch the opponent.
Double-Edge is much stronger, but cannot flinch the opponent, and has recoil damage.