Bowser's Castle Court
From the Super Mario Wiki
Bowser's Castle Court (Bowser Castle Court in-game) is an unlockable court set in Bowser's Castle in the game Mario Power Tennis. The standard version of the court is a platform suspended over a pool of lava by large chains. Mecha-Bowser watches over the court, and can be seen in the background. In the gimmick version of the court, the court tips when players move around, making it difficult for them to keep their footing. This also lowers ball-control, and it is very difficult for players to hit the ball in the court. The stage can be unlocked by beating any Tournament in the Singles Tournament. It is also the home of the minigame Mecha-Bowser Mayhem. It is unlocked by winning the Fire Cup in singles.