Behind The Waterfall

Behind The Waterfall is the name given to a supposed level found by using the Wing Cap on the roof of the castle and flying into the waterfall. This is also the name given to the Super Mario 64 DS version of Cavern of the Metal Cap. Some people believe that Yoshi or Luigi is inside this level, and others just believe it is an alternate entrance to Cavern of the Metal Cap.

Hammer Bros.
There is a rumor that there is a 120-star door behind the waterfall that when opened, will lead to a Hammer Bros. boss fight. They will act the same as they do in their other appearances in the Super Mario Bros. series. They jump around the arena and throw hammer projectiles at the player. In this appearance, they are defeated by being ground pounded on the head 3 times for each Hammer Bro. Defeating them can give a 121st star, Luigi, Yoshi, or a new ending.