Doom 3

Skip checkpoints:
Hold L and press B, A, X, Y during game play to advance to the next checkpoint. A sound will confirm correct code entry.
Nick Gravelyn, and Taylor Martin.

Invincibility:
Hold L and press X, Y, B, A during game play. A sound will confirm correct code entry. To confirm that it is enabled, fire any weapon with splash damage at a nearby wall. 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-enabled to regain its effect.
Jonz0r, ATRAY43, and batsofdarkness.

Doom Ultimate and Doom 2: Cheat mode
Enable one of the following codes during game play. A sound will confirm correct code entry. Repeat the code to disable its effect. Note: These games are only available in Doom 3: Collector's Edition.

Doom Ultimate and Doom 2: Toggle God and Degreelessness mode:
Hold L and press A(4).
Steve and Larry.

Doom Ultimate and Doom 2: All weapons, ammunition, and armor:
Hold L and press B(4).
Steve and Larry.

Doom Ultimate and Doom 2: All weapons, health, keys, and armor:
Hold L and press A, B, A, B.
Frank Macias.

Doom Ultimate and Doom 2: Temporary invincibility:
Hold L and press X(4).
Steve, Larry, and samman.

Doom Ultimate and Doom 2: Full map:
Hold L and press Y(4).
Steve.

Doom Ultimate and Doom 2: Berserk mode:
Hold L and press X(3), Y.

Doom Ultimate and Doom 2: End level:
Hold L and press A(2), B(2).

Doom Ultimate and Doom 2: Chainsaw:
Hold L and press B(2), A(2).

Doom Ultimate and Doom 2: Invisibility:
Hold L and press X(2), Y(2)

Doom Ultimate and Doom 2: Light Amplification Goggles:
Hold L and press Y(3), X.

Doom Ultimate and Doom 2: Radiation Suit:
Hold L and press X, Y(3).
arotac uwbo, nonetr.

Doom Ultimate and Doom 2: Walk through walls:
Hold L and press A, B, Y, X. This is useful with the more difficult "impassable" levels. It also works under the nightmare difficulty setting.
tyson whitesides.

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

Hint: Cabinet combinations:
Jason Voorhees, Soadkidlen, Chad, and logan miller.

Cabinet 001: 396
Cabinet 003: 483
Cabinet 009: 752
Cabinet 013: 586
Cabinet 017: 347
Cabinet 023: 531
Cabinet 038: 409
Cabinet 039: 102
Cabinet 047: 123
Cabinet 048: 123
Cabinet 049: 123
Cabinet 054: 246
Cabinet 054 (second): 142
Cabinet 063: 972
Cabinet 064: 651
Cabinet 078: 364
Cabinet 079: 364
Cabinet 103: 259
Cabinet 104: 579
Cabinet 112: 538
Cabinet 114: 715
Cabinet 116: 972
Cabinet 116 (second): 624
Cabinet 117: 624
Cabinet 213: 371
Cabinet 215: 298
Cabinet 216: 624
Cabinet 217: 624
Cabinet 317: 841
Cabinet 386: 836
Cabinet 387: 836
Cabinet 452: 571
Cabinet 666: 372
Cabinet 669: 468
Cabinet 21D: 298
Martian Buddies 1 and 2: 0508
Weapons Storage 1 and 2: 584
Monorail Override Junction 5: 826
Monorail Override Junction 5 Junction 7: 953
Plasma storage code: 734
Chief Abrams Office: 931
Locked doors in Lab A: 627

Hint: Defeating the final Boss:
When you each the end Boss, do not bother wasting your ammunition on him. Just stay away from him. Kill the Imps and other demons and use the Soul Cube on him. If you are play in co-op mode, shoot him. Use the Soul Cube on him about five or six times. On the last time you will see an intermission sequence of him dying.

Hint: Defeating teleporting demons:
When a demon teleports (generally signaled by whisperings, a red tint throughout the screen, and red lightning in the location where they will always 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

Hint: Defeating Archs:
In the "Security Monitoring" area, there are several enemies including Archvilles and they bring Cherubs to kill you. Run to the door at the far right and stay on the "blocks". The enemies will not attack you (life and armor are full and the Arch keep walking without attacking). You can now take out your chain saw (to save bullets) and use it to kill the Achs and Cherubs. [Screenshot]
Thi.

Hint: Defeating demons:
The best way to kill demons is to use the plasma gun. The plasma from the weapon can cancel the demon's plasma balls that are often thrown at you. Because the plasma gun is rapid fire, it will just keep firing until you release the trigger.
Bert Godfrey.

Hint: 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.
Madison Nash.

When you are fighting the Guardian boss at the end of Hell, make sure you save some rocket launcher ammunition and at least four BFG cells. Note: When you kill the Guardian you will lose all of your ammunition and guns -- there is no point of holding back and trying to save ammunition. When you first see the Guardian, use the rocket launcher to destroy all of its Seekers. As soon as you kill the last one, charge up the BFG until four BFG cells are charged into one shot. Fire it at the blue light above the Guardian's head and it should die instantly. If done correctly, you can kill it within twenty seconds without losing any of your health.
FreakVan.

Hint: Defeating Sabaoth:
Note: A charged Soul Cube is requried for this trick. As soon as you enter the room with Sabaoth, the door in front of you will open and he will say "Welcome to mess hall". Fire the five rockets and you might detonate the BFG shot that he fires. After firing the five rockets he will be very close to you. Stand still and fire your Soul Cube to defeat him. Note: This was done under the normal difficulty setting.
Thi.

Hint: 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.
Information in this section was contributed by Madison Nash.

Use the following trick to kill the new and improved Sarge much easier. The key is to use the chaingun. It will blow up his BFG bullets in his face. It will take about thirty seconds to kill him in this way, and you do not have to use the Soul Cube. There is is a video disc that you will get just before you fight him that explains the BFG, and says that small arms fire will blow up the chip in the ball of energy, making it explode instantly.
Cthulhu911.

Hint: 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.
Robert Essen.

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.
Kyle.

When Imps shoot their energy ball at you, crouch underneath it and run at them. Then, pump them in the face with the shotgun.
Baconlover.

Hint: Mars City Underground: Save ammunition:
When at the end of Mars City Underground, kill the scientist using the flashlight. After the intermission sequence, hit him a few times until he explodes, changes into a skeleton, and deteriorates. This saves ammunition and health. Do this before he turns into a zombie.
Heath Bradshaw.

Hint: iD Software PDA:
In the last level, just before you see the intermission sequence before the devil, instead of going to where the sequence begins the fight with the devil, go left. By the candles should be an ID Software symbol on the wall. Go towards the brick until you are touching it (you may have to duck). Press Action (R) when your crosshairs are over it. The brick will go inside the wall, and the wall behind you to the left will open. In that room will be a special PDA from iD Software, saying thanks for playing Doom 3 and other things. You can then fight the devil.
Zachary Love.

Get to the point during the last level at the end before you face the Cyber-Demon. Instead of facing the Cyber Demon, go to the left of where the rocks open up. Go under this rock and it would say, "id". Select it, then look to the left. Rocks will open. Go inside to get a PDA. It will read "id Software all security clearance". All doors will now be unlocked.
Gorefish.

Hint: 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.

Hint: Save scientist:
In Delta Labs Level 3 South, almost as soon as you enter a room, you will see a zombie marine shooting a scientist. It is possible to save him using the Soul Cube in nightmare mode. Make sure you have the Soul Cube charged. As soon as you enter the room, use the Soul Cube on the marine. The scientist will be unharmed and run away. You must be very quick when you do, and it may require a few attempts.
Insomniac515.

Hint: 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.

Hint: BFG:
At Chief M. Abram's office, the BFG is in the test chamber when you are there to retrieve the plasma inducer. You will see the BFG in a test chamber in a room that is locked. Enter 931 as the code to get the BFG.
Azz Killer.

Hint: Enpro Plant Sector 2 plasma room door code:
The door code for the plasma room in Enpro Plant Sector 2 is 734. Be careful; leaving that room causes several creatures to transport directly outside the door, but it is worth it.
Michael Austin and Netlocust.

Hint: Locker 666 warning:
When you find locker 666, do not open it. There is a monster in it along with security armor. The code is "372".
Cody Weddle and k lester.

Hint: Strange teleporting demon death:
When fighting a teleporting demon and he teleports go to the place where he is going to, bring out the shotgun/ When the red circle appears, shoot it. He will die inside the circle.
Richard.

Hint: Safety from enemies:
To be almost invincible equip the chainsaw, hold R, and run forwards. Anything in front of you will die in a few seconds. This works for all enemies, but not especially well on enemies with ranged attacks. It works best on Zombies, Imps, Cherubs, Maggots, Wraiths, and in dark areas.
k lester.

Hint: 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.

Hint: Punching bag:
After defeating the spider Boss, go to southwest part of the area. There will be a dangling body that you can punch as many times desired.
FeverFour.

Hint: Hidden message:
Go to Delta Labs Sector 4. When you get to the room with the second chainsaw zombie, kill him, then face to the door that leads into the teleporter room. Look to the left. You will see a skeleton sitting in a corner. Hit it out of the corner and you should see a message written in black, reading "YOU LOUSY IT WORKS".
Matt.

Hint: Classic Doom reference:
When you get to Mars City, go to the kitchen. Look closely at the video game in the back to see a classic Doom screen while you punch the turkey.

In the last few levels are stone tablets that feature the original Doom cover.

Glitch: Into the Hell hole:
Play the Primary Excavation level. Enable the "Invincibility" code. When you fight the Cyberdemon, jump into the hole where the Imps and Maggots are coming from. You will fall for awhile until you get to the end, which is just where the hole comes to a point. You must restart the level to exit.
Corey Dane Hoster.

Glitch: Devil death trap:
Enable the "Invincibility" code. When fighting the Devil, run behind him and stay in the right corner. Turn around and continue to riddle him with bullets. Eventually you will be driven up the wall were the Devil will stop attacking. You will continue to be killed but cannot move.
Michaell Michaud.

Glitch: Kill Counselor Swan and bodyguard and get the BFG early:
During the "Alpha Section 1 West" level, when you find the scientist with the PDA go past the glass crushing thing. You will find the lost PDA. Drop down the hole and open the door. Run to the next room and kill the two enemies. When you reach the next room, shoot the two blue glass tubes with the two monsters in the room. Note: Enable the "Invincibility" code. Shoot the tubes and they will burst into flames instantly, killing every enemy around you. Look to the left into the room with the big window. You will see Counselor Swan and his bodyguard running, and the flames will kill them. Go into the room where you saw them and the BFG 9000 will be on the ground. Do not use its ammo and go on to the next level. Go into the bathroom so you can see yourself in the mirror, then pull out the BFG. It will just be a black box in your hand and you cannot see it. Also it will shoot boxes and explode.
Tim Storey.

Glitch: Fight Cyber Demon outside the ring:
Enable the "Invincibility" code during the last level and get to the Cyber Demon. After the intermission sequence you will be on his right-side. Instead of running around in circles starting from his right side, move to his left side as soon as the intermission sequence ends. Run backwards clockwise until you reach the 3 o'clock position. Let him hit you to fly out the ring. You will be on the lava and fire ground. Run back to the 3 o'clock position and look for the Cyber Demon. Normally he sees you no matter what, but if he does not, shoot him to get his attention. Let him shoot you numerous of times or dodge his rockets. Make sure you keep watching him. Between one and two minutes of him shooting you while you are outside of the ring, the Cyber Demon will teleport. Run on the other side of the outside ring. You should see the Cyber Demon walking in mid-air, still shooting at you. He can move and walk in your direction -- you really cannot hide from him. He cannot step on you, but you can shoot under him. No Imps or other demons can fight you while you are outside the ring .
khambrel wade.

Glitch: Get Jack Campbell's BFG 9000:
Go to Alpha Labs Sector 1 West and enable the "Invincibility" code. Enter the Hydrocon lab (the room with the two big tubes). Quickly shoot one of the tubes and it will explode. Quickly look in the window in front of the tubes to see jack dying. You can now get his BFG 9000. If this does not work at first, try it again faster.
Eric Bouchard.

Glitch: Disappearing person:
Play a co-op game on Xbox Live, In the room with about two or three pretty big Pinkeys (they walk on all fours), there should be a person lying against the wall. On one screen, it should be there. On the other screen, it is not.
John Costanzo.

Glitch: Chainsaw zombie:
In Delta Labs Number 4, after you go through the bay door that Betruger went through you will enter a hallway splattered with blood with the words "suffer" and "die" written on the wall in blood. In one of the long and empty hallways, the lights go out as you walk down it. A chainsaw zombie will appear for about half a second, then disappear. It will do this all the way down the hallway until you reach the door and fight it.

Glitch: Bloody bullets:
Find an non-exploding drum of chemicals. Get a demon in front of it. When you kill it, continue shooting. The drum will get covered in blood instead of holes and singes. The machine gun works best.
Michaell Michaud.

Glitch: Woman's corpse:
The first time when you see the flying skull, it should be coming out of a woman. Her PDA says that she works on the plasma gun project. The locker has a plasma gun in it. However, the girl's corpse should still be there. Hit her with a flashlight and watch her shake. She never goes away.
ThunderBritches.

Glitch: See Mars City:
Go to the Communications Transfer Site 1 . Get to the Mar's surface (outside) and enable the "Invincibility" code. Kill all the spiders. Get to the lift but do not ride it. Instead, go to your left and jump down the hole. Take out your flashlight and look at the corner of the wall. You will see a passage. Go in it, and you will be in a hall. Go all the way forward of the hall then go right until you reach the wall. Then, go to the corner of the location and you will see Mars City.
Eric Bouchard.