Enter code at the start menu

At the title screen, press Select to access the configuration menu, then press Start. At the Options Menu, hold the following on Controller 2:

X + A + L + R

Then on Controller 1 press Start

Press Option + 6 to raise or Option + 9 to lower.

Hold Pause with Option and keep them pressed during the entire process. Press 1+ 3. Then press 2 + 5 + 7 + 9. The Predator will laugh to confirm the cheat code entry.

Begin a game, then press Pause, Option, 6, 1+3, B, A, 9, A, 9, A, *, Option, 6, #, *, *, Option, 2, Option. The Predator will laugh to confirm the code. Hold Option and enter any of the sequences below.

General:
A - Next Floor
B - Previous Floor
5 - God Mode

As the Marine:
1 - Shotgun
2 - M14-A Pulse Rifle
3 - Flame Thrower
4 - Smart Gun
1+2+3+4 - Refill Ammo
8 - Motion Tracker
6 - Raise Security Level
9 - Lower Security Level

As the Predator:
1 - Combi Stick
2 - Shoulder Cannon
3 - Smart Disc
4 - Wrist Blade

As the Alien:
1 - Tail Attack
2 - Claw Attack
3 - Extending Mouth

You must first activate cheat mode (hold pause + option, press 1 + 3, then press 2 + 5 + 7 + 9). Then enter the cheats any time.