Duke Nukem 64
Cheat Menu

At Title Screen, press Left, Left, L Button, L Button, Right, Right, Left, Left.

Level Skip

At Title Screen, press L button, L button, L button, C-Right, Right, Left, Left, C-Left.

All Items

At Title Screen, press R Button, C-right, Right, L Button, C-left, Left, C-right, Right.

God Mode

Press the R Button 7 Times and Then Press Left on the D-pad. You should hear a sound. Now go to the Cheat Menu and there it is at the very top.

Monster Toggle

At title screen, press L button, C-Left, Left, R button, C-Right, Right, Left, Left, Right You should hear a sound. There should be a new option in the Cheat Menu.

Unlimited jet pack fuel
Enable the "All items" code while flying with the jet pack.

Drink to your health

Shoot or blow up a water fountain, fire hydrant, or even a toilet. Then walk over to the water that's squirting up and hold "A". You will gradually regain your energy.

Big Duke/Little Duke

For Big Duke, you must have invincibility. Then...

This process works with the Shrinker for Little Duke.