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.
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.
To use the grenade launcher, go to Assault on the Kallos and press up twice on the D-Pad and you will be on it. This can be done at any level because it's on a default loadout. Now you can have plenty of fun with the "noob tube."