If you type in the classic password Up, Up, Down, Down, Left, Right, Left, Right, B, A at the "Touch Start" screen you will see the super secret Secret Screen!
If you put the Sea Salt item on the Milkshake item, it will restore all of your health as well as do a Star of Frozen Rains attack!
If you complete the game in New Game + mode, you unlock the Music Viewer! Use this to listen to all of your favorite songs!
If you beat the game, you unlock New Game + which allows you to restart the story while retaining all of your stat improvements and items. Mathematical!
Use the Beauteous Wings item in Chet's cell at Lemongrab's dungeon to find this one-of-a-kind item!