Super Mario 64/Cavern of the Metal Cap

This stage is found in Hazy Maze Cave. To get there, get to the underground lake, then ride the sea monster to the door that is not blocked by grating. In the room beyond is a portal leading to the stage.

There are two stars in Behind the Waterfall. One is located above the ? block in the platform at the end. You will need Mario to hit the block, then float up. The other is found by getting the red coins. It is recommended you try this as Wario, since there is a strong water current, and 6 red coins are found around the aforementioned platform. Wario's metal ability lets getting those a breeze. The other two are close to the Bob-Omb buddy.

Note: If the water current pushes you out of the level, you will end up outside the caslte where the waterfall is. If you get a star, you will end up outside the entrance to Hazy Maze Cave.