Chicken Experiments
Anywhere in the game that you can manage to fall off the main game map, you will be teleported to the chicken experimentation room. Note: You cannot get out without restarting the XBox. Some ways to get into the room include:

Sweetsville factory
Unlock the low gravity cheat and jump on the roof of the building that holds the power switch. Jump off into the water behind it.

Prince Charming's Castle
Jump out of the window that you are supposed to kick the prisoners out of.

Invincibility
At the Title screen, press Up, Down, Down, B, A, A, Z, Down, Up, Left, B.

Cheats
Perform at least four good deeds to unlock race mode. Play in race mode to get tokens to buy and unlock the following cheats: Chalk Mode, Crude Oil Mode, Cyber Shadows, Fast Mode, Infinite Flame, Infinite Gas, Invulnerability, Leak Mode, Low Gravity, Money For Merlin, Plastic Mode, Super Flatulence, and Super Strength.

Creepy Crypt
Doing 5 good deeds will unlock the Creepy Crypt.