CPU control:

Hold L1 + R1 and press Up, Left, X, Left, X, Down, Right, Circle, Right, Circle during game play. A sound will confirm correct code entry. The game will continue by itself under CPU control.

Alternate game:

Successfully complete the game, then load the saved game file and select any level. Game play will begin with new routes at a harder difficulty setting.

Fiery Ulala:

Achieve a rank of 95% or higher to play as Ulala surrounded by purple fire.

Michael Jackson cameo:

Michael Jackson can be found in the last level of the game.

Hint: Defeating the second-to-last Boss:

When facing the Boss that makes you copy its moves in reverse, simply turn your controller upside-down -- you will not have to think the reversed commands.

Thanks to mdilay6969