From the Super Mario Wiki
The Wario Punch is a Special Move in the Gamecube game Wario World. To execute this extremely basic move, the player must simply press the Button, allowing Wario to shoot out his fist, damaging enemies in front of him. By holding the Button down, a Punch followed by a Dash Attack will occur. While beating up an enemy or a group of enemies, every third punch will be an extremely powerful headbutt.