• First throw all your bullets then press and hold R, L then press x,b,b,x,y,y,y,a,a,x,x,a,y,b,x and you will have infinite ammo

Bathroom scare - After you have found the lost scientist and are returning to the main building, find your way back to the bathrooms. Stand in front of the mirror with your pistol then cycle through until your shotgun then get very close.

Bypass Checkpoints

Hold L and press B, A, X, Y during gameplay.

Cheat List for Ultimate Doom and Doom 2
These are the Ultimate Doom and Doom 2 cheats, which are only included with the Limited Edition Doom 3 game -

All Keys, Weapons and Ammo - Hold down (L) and press (A), (B), (A), (B).
Berserk Mode - Hold (L) and press (X), (X), (X), (Y).
End Level - Hold down (L) and press (A), (A), (B), (B).
Chainsaw - Hold down (L) and press (B), (B), (A), (A).
Weapons and Ammo - Hold down (L) and press (B), (B), (B), (B).
GOD Mode - Hold down (L) and press (A), (A), (A), (A).
Invisibility - Hold down (L) and press (X), (X), (Y), (Y).
Light Amplification Goggles - Hold down (L) and press (Y), (Y), (Y), (X).
Radiation Suit - Hold down (L) and press (X), (Y), (Y), (Y).
Show All Map - Hold down (L) and press (Y), (Y), (Y), (Y).
Temporary Invincibility - Hold down (L) and press (X), (X), (X), (X).

God Mode - Hold L and press X, Y, B, A during game play. A sound will confirm correct code entry. Note - The code cannot be enabled until you take the elevator after being attacked at the start of the game. When a new area is loaded, the code must be re-entered to regain its effect.

Defeating the Guardian Of The Soul Cube - When fighting the Guardian Of The Soul Cube in hell, do not bother shooting his body. This is a waste of precious ammunition. Instead, blast his "searchers" with something with good coverage like the chaingun, and he will have to spawn more. When he does, a blue light will appear over his body. Shoot it with the rocket launcher. Do this a few times and he will die easily. Also, look in the room around the columns for ammunition, health, etc.

Defeating Sarge - Be prepared to die a few times. Beware of the edge of the room, as you can fall off. Also, do not hide behind the pillars for too long. They will open up and arc electricity periodically. When you walk into the room, a giant bay door at the opposite end of the room will open, revealing the "new and improved" Sarge. As soon as that door opens a crack, start lobbing rockets in there. After you score about six good hits without being splattered by his BFG, break out the Soul Cube (that you should have charged before entering the room) and let him have it. It should kill him and heal you. Pick up the armor and ammunition around the room before continuing.

Defeating Imps - If the Imp is jumping at you, blast it while it is in the air with the shotgun to kill it in one shot. This is slightly difficult to time.

As soon as an Imp has thrown a fireball at you, strafe around it with your shotgun equipped. Get very close to the front of the Imp and blast it in the chest. About 95% of the time, the Imp will die.

Defeating teleporting demons - When a demon teleports in (generally signaled by whisperings, a red tint throughout the screen, and always red lightning in the location where they will appear), you will have a split second before they are able to attack. Take a good weapon (for example, a shotgun or chainsaw for imps and wraiths) and stand close by. For powerful creatures, such as Pinkys, use a ranged weapon and stand at a safe distance. Remember to save the game often

Kill the maintenance workers in the beginning of the game - It IS possible to kill those workers before all hell breaks loose. Equip your flashlight, stand close to a worker, then turn away just enough so the “talk” option is no longer available, swing it, then turn back as quick as you can. If you time it right, the flashlight will make contact & kill them in one hit [it might also help if you turn up your turn sensitivity], and you’ll have less zombies to face later on.

Locker Combinations:

Locker 001 - 396
Locker 003 - 483
Locker 009 - 752
Locker 013 - 586
Locker 017 - 347
Locker 023 - 531
Locker 038 - 409
Locker 039 - 102
Locker 047 - 123
Locker 048 - 123
Locker 049 - 123
Locker 054 - 246
Locker 054 (second) - 142
Locker 063 - 972
Locker 064 - 651
Locker 078 - 364
Locker 079 - 364
Locker 103 - 259
Locker 104 - 579
Locker 112 - 538
Locker 114 - 715
Locker 116 - 972
Locker 116 (second) - 624
Locker 117 - 624
Locker 213 - 371
Locker 215 - 298
Locker 216 - 624
Locker 217 - 624
Locker 317 - 841
Locker 386 - 836
Locker 387 - 836
Locker 452 - 571
Locker 666 - 372
Locker 669 - 468
Martian Buddies 1 and 2 - 0508
Weapons Storage 1 and 2 - 584
Monorail Override Junction 5 - 826
Monorail Override Junction 5 Junction 7 - 953

Nightmare mode - Complete the game once under any difficulty setting. When you start on Nightmare Mode. you will start with the Soul Cube.

Pumped up Soul Cube - After you acquire the Soul Cube, equip it and wait about one to two minutes. It will reveal its blades and spin for a very short time.

Saving ammunition - If you can avoid it, try not to use weapons like the shotgun or others that have difficult to find ammunition on the weaker zombies. The flashlight (if you are fast enough) or just the pistol usually will suffice.