Hidden Invasion Cheats (PlayStation 2)

At the title screen, rotate the D-pad clockwise 4 times. A sound will confirm the code.
When you play the game, most of the things in the area will bounce all the time.

At the title screen, press Up, Down, Down, Up, Left, Left, Up, Right, Right, Up, Up, and
Up. A sound will confirm the code. The game will be a little easier.

At the title screen, press Left, Left, Up, Up, Right, Right, Down, and Down. Begin the
game and all the players and enemies will have big heads and deformed bodies.