When you face the boss, it makes you copy its moves in reverse. An easy way to make this easier is to turn your controller upside down and then play him. You won't have to think of the reverse commands.
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 CPU will now take over for you for the rest of the game.
In the last level of the game, you can see Michael Jackson make a cameo appearance.