South Park

Enter MAJESTIC as a code.

Enter OMGTKKYB as a code.

To enable all characters in multiplayer mode, enter the password OMGTKKYB. That, as any South Park fan will know, stands for "Oh My God, They Killed Kenny! You Bastards."

Enter BOBBYBIRD as a code. Note: Enter ZBOBBYBIRD in the EU/PAL version of the game.

Enter FATKNACKER as a code.

Enter OUTRAGE as a code.

Enter MEGANOGGIN as a code.

Enter LOVEMACHINE as a code.

In multi-player mode if you get shrunk, get an invincibility can just before you get big again. You will stay shrunk for the remainder of the game, even if you die.

Whenever Ultra Mega Mega Man run backs to get more health, go over to the platform where he charges up. Hit the button on the right when it starts blinking to prevent him from recharging.
When fighting Ultra Mega Mega Man, shoot him three times with the Super Sniper Chicken (which is provided for you in his "lair"). When he starts to spaz out and lower his head, wait until you see him walking towards the power station in the corner of the room. Get right behind him, and after about three to four eggs to his power pack, Ultra Mega Mega Man will be no more. This way, you do not have to keep shooting the large octagon-shaped button to stop his recharge process. Even if you do this, you will still have to shoot him in the back anyway, and he will still try to recharge.
Hit Ultra Mega Mega Man with Terrence and Philip dolls until he goes back to his stand. Shoot the target next to the robot before he is done recovering and repeat until he is defeated.