From the Super Mario Wiki
The first part of the level features a loop arena with different platform elevations. Four Lava Bucklers and two Lava Smashers inhabit the lower platform, while two Lava Peek-a-Boos and Lava Valkyries each are scattered around the higher platform.
The second part of the level features an arena where Mario and co. must face Bwario and Bwaluigi. They are on the elevated platform, with two Lava Smashers and Lava Valkyries each.