Enter the following codes at the Main Menu:

Master Code:
X, L, X, L, X, X, L, R, X, L, X, L, X, X, L, R

Debug Mode:
X, X, L, L, L, L, X, X, L. Pause during play to access the debug menu.

Level Select:
X, L, X, L, X, L, L, R

All Costumes:
L, X, L, X, X, L, R

All Cerebro and FMV:
X, L, X, L, X, X, R, L

Thanks to Revolution readers Rob Deagle, Anthony Russillo, and BunsenBurn!