Thunder Cast Shot
From the Super Mario Wiki
The Thunder Cast Shot is Wario's Offensive Power Shot in Mario Power Tennis. Wario pulls out a machine with a small Hammer attached and hits the ball. This looks like a normal shot, but it is actually powerful and leaves the opponent shocked. When shocked, the opponent has two seconds to react before a shock-wave hinders their shot. The shock goes away after about three shock-waves. The shot also causes the opponent to lose a Power Shot they may have stored. Its recovery time is somewhat slow.