The Lava Pit

From Mario - Wiki on Neoseeker

This is in a lava pit, you play on rock. The stadium is rocky, and occasionally a fireball or fireballs will land on the stadium causing a huge put of lava. Avoid it at all costs as it will burn your characters and make them run round franticly for a short period of time. To unlock this stadium in domination mode beat it in the fire cup.