Duke Nukem 64 Switch monsters off: Go to the cheat menu (to get the cheat menu it self do this code on the main menu: LEFT, LEFT, L, L, RIGHT, RIGHT, LEFT, LEFT. Now you can get in the cheat menu.) Then hit these buttons in this order: L, LEFT C, LEFT, R, RIGHT C, RIGHT, LEFT, LEFT, RIGHT. You will here a siren if you did the code correctly. Then go in the cheat menu and now you can turn the monsters on and off. Invincibility: To get the invincibility code players must first enter the cheat menu code ( Press the following at the main menu to access the hidden cheat menu: LEFT, LEFT, L, L, RIGHT, RIGHT, LEFT, LEFT. Now the cheat menu will be accessible). Then simply hit R button seven times in a row and then press left on the directional pad. A sound should signify that it worked. Now go into the cheat menu and turn invincibility on. Cheat Menu: At the main menu: LEFT, LEFT, L, L, RIGHT, RIGHT, LEFT, LEFT.