Whirluigi is Waluigi's Offwnsivw Power Shot in Mario Power Tennis. Waluigi Jumps in the air in the shape of an upside-down L and spins around. This causes the ball to greatly curve over the net and knock the opponent back a few feet. It also causes them to spin around crazily, hindering their movement. It also can cause the opponent to lose any Power Shots he or she may have stored. Recovery time is great.
According to this, Waluigi may have some dancing skill also proven in Dance Dance Revolution: Mario Mix.