Enter <477MYFR13NDS4R3SP13S> as a case-sensitive code. Big Head mode will now be on in Local Multi-Player games. Reset the game to its default options to return to normal.
Change weapon loadouts in Multiplayer (Split-Screen) matches
Hold 2 and press Left or Right on the Nunchuk or D-pad.
Hold Minus and press the Left Analog-stick or D-pad Left or Right on a Classic Controller or Pro Controller.
Hold Z and press A on a GameCube controller. The scoreboard will appear. Then, press Left or Right.
Invisibility mode
Enter Inv1s1bleEv3ryth1ng as a case-sensitive code. The "Invisibility Mode" will be unlocked in the "Multiplayer Split-Screen" section of the "Modifiers" menu. Press B during game play to become invisible instead of sprinting.
Multi-player weapons and gadgets
Reach the indicated level in multi-player mode to unlock the corresponding item.
This technique takes some practice. As you wait for your gun to go through most of its reload animation, move forward and sprint just before it ends and you'll end your reload faster. This has no effect during the main campain mode, but works in multiplayer. This might not work with all guns.
Tag mode
Enter NotIt!!!11 as a case-sensitive code. The "Tag" option will be unlocked in the "Multiplayer Split-Screen" section of the "Modifiers" menu. Tag mode requires three or more players.
Wilhelm Scream
In the Facility Level, after blowing up the fuel tanks, you can hear one of the soldiers do the Wilhelm Scream. GYAAAAA!!!