View Credits
On the title screen, press C, B, A, A, B, C, Y, Z, X, Down, Down, Start.
Sound Test
On the title screen, press X, X, Y, Y, Z, Z, A, A, B, B, C, C, Start. Press Left or Right to choose a sound.
Bonus Game
For a friendly game of Staff Ball, go to the title screen and press X, Y, Z, X, Y, Z, C, B, A, Up, Down, Start.