From the Super Mario Wiki
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Whirluigi is Waluigi's Offensive Power Shot in Mario Power Tennis. Waluigi jumps in the air in his signature Γ shape and spins around, generating a cyclone around him, and hits the ball with it. 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, which is also seen in Dance Dance Revolution: Mario Mix.
Waluigi Special Shot in Mario Tennis Aces (called Showtime in the game) is very similar to the Whirluigi technique. The only difference is Waluigi showing off by putting a rose in his mouth (a taunt he started to use in Mario Party 8).