Headbutt is an attack in the Super Smash Bros. series that Donkey Kong can perform. It's his side B attack, and will cause Donkey Kong to headbutt an opponent. If done correctly, the opponent will be planted in the ground for a short time. The player can escape by wiggling the control stick, or just waiting.
Normally, it is used to trap opponents in the ground for a short time. This time it is often used to set up for a Giant Punch or a Smash Attack. If used against an opponent while in mid-air, the attack acts as a Meteor Smash, sending the opponent down. If they hit the stage, they will not get buried.
Another use, albeit with limited effect, is to slow Donkey Kong's decent. When using this attack in mid-air, Donkey Kong only falls marginally and heads to the direction in which he is facing a bit. It can be used repeatedly like this, but the horizontal distance is not that much.
In Super Smash Bros. for Nintendo 3DS / Wii U, moves have two additional variations to be customized.
The first customization for Headbutt is a much slower version. The compensation for this slower version is that the move has Super Armor that prevents Donkey Kong from stopping the animation because of an attack.