Successfully complete either bonus level to unlock songs in the music box option.
Complete all the fairground levels to unlock a new area that allows you to battle previously defeated bosses.
Press start on the 2P controller and press square to make Popka make you go super high.
Complete all of the fairground levels to unlock an option for a picture gallery
In order to unlock a picture for the picture gallery, you must acquire 150 dreamstones or more in a single stage. Once you have done this, visit Momett's House to view the picture in the photo album section. To unlock every single picture, collect 150 dreamstones in all stages (including Momett's Chamber o' Horrors and Chamber o' Fun).
Hurdy Durdy, the music box, can be completely unlocked by doing two things. First, you must make sure to have already unlocked the Chamber o' Fun and the Chamber o' Horrors. Once you have done this, successfully complete the Chamber o' Fun to unlock the Hurdy Gurdy option (found at Momett House) with half the games songs accessible in it. Now complete the Chamber o' Horrors. Once completed, you will unlock the second and final set of songs for Hurdy Gurdy.
Finish the game to unlock Mometsuto as a playable character.