Fire Breath (Power Shot)
From the Super Mario Wiki
Fire Breath is the Offensive Power Shot used by Bowser in Mario Power Tennis and Mario Tennis: Power Tour. Once the Power Shot is activated, Bowser will use his Fire Breath to set the ball on fire, then hit the ball down the court in flames. If returned, the receiver will be pushed back drastically, similar to other Offensive Power Shots such as Barrel Cannon Blast.