Easy mode
At the title screen, press Up, Down(2), Up, Left(2), Up, Right(2), Up(3). If you entered the code correctly, you will hear a sound.
Big heads and deformed bodies
At the title screen, press Left(2), Up(2), Right(2), Down(2). If you entered the code correctly, you will hear a sound. Start a game and all players and enemies will have big heads and deformed bodies.
Oogie Boogie mode
At the title screen, quickly rotate the Left Analog-stick counter-clockwise four times. If you entered the code correctly, you will hear a sound. Many objects will be bouncing during the game.