Select "Options" at the main menu, then select "Game". Press Right(2), Left, Right, Left(2), Right at the Game Options menu. The screen will return to the main menu to confirm correct code entry. You now have access to the Debug Game mode, where you can pick any level/mission and select any scene after the major loading scene of the mission. As well as Debug Game mode, if you go back to the options menu after the code enabled, and before you start a game, a new "Cheats" option is now available. The "Cheats" menu has options for "Unlimited Ammo" and "God Mode". After activating either or both options, you can start a new game, continue a game, or play Debug mode.