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.
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.
Code for god mode
Hold the left trigger and press: X, Y, B, A a sound of a demon will confirm the cheat.
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 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.
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.
Doom Ultimate and Doom 2: Cheat mode
Enter one of the following codes during game play. A sound will confirm correct code entry. Repeat the code to disable its effect.
Doom Ultimate And Doom 2: Toggle God And Degreelessness Mode
Hold L and press A(4).
Doom Ultimate And Doom 2: All Weapons, Health, Keys, And Armor
Hold L and press B(4).
Doom Ultimate And Doom 2: Temporary Invincibility
Hold L and press X(4).
Doom Ultimate And Doom 2: Full Map
Hold L and press Y(4).
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).
Duck Hellfire
The projectiles thrown by the imp and hellknight can be ducked if you time it correctly (it will do no damage). Naturally, you want to do this against enemies on the same height as you, not on shots coming at diagonals.
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.
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.
Kill the maintenance workers
It is possible to kill the 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 and kill them in one hit. It might also help if you turn up your turn sensitivity.
Killing 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.
Killing 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.
Killing the Cyberdemon (Last Boss)
When you start out,pick up all the ammo you can find.Then,when you find the Cyberdemon, sprint away from him (L).Then get out an-easy-to-kill weapon like a B.F.G. or rocket launcher or chainsaw.Then,pay attention to the big hole in the center.Whenever a demon pops out of it,shoot it.Kill 5 demons and then throw your soul cube at the Cyberdemon.You'll need to kill it with 4 soul cube throws so kill 5 demons then throw the soul cube at Cyberdemon and continue this sequence 4 times and he'll die(on recruit difficulty on nightmare i think it's 5 or 6 times.)
But beware of his rocket launcher,he does 50 damage per shot on you on recruit,so it would probably be a instant kill on nighmare. Beware of his feet,if he stomps on you,he'll kill you instantly.If you have invincibility on,if he stomps on you, you'll fly away and you won't get back over there.To avoid these horrible accidents,stay as far away as possible from him.To avoid getting caught up with him,sprint away from him(L)(You have unlimited spint in that level.)
Level Skip
Enter your PDA, the select 'Objectives'. Hold L and press B, A, X, Y. Exit the PDA to advance to the next level.
Machine gun and shotgun on 1st level
If you want a machine gun and shotgun on the 1st level you must get to the checkpoint where the guard 1st gives you the pistol armour flashlight etc after hell has broken loose. When your using the computer to open the security door underneath the button should be a small panel. Click it then click unlock door 1. this will allow you to get the machine guns and shotgun you saw the 1st time which apart from the shotgun you wouldn't be able to get laster in the game. Getting these weapons will spawn 2 imps but with the new guns its easy.
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.
Skip checkpoints
Enter your PDA, then select "Objectives". Hold L and press B, A, X, Y. Exit the PDA to advance to the next checkpoint.
Super Turkey Puncher Three
Go to the first level in Co-Op mode and proceed through the level until 'Command Access Junction'. There you can find two Super Turkey Puncher arcade machines made by 'Nabcon'. On the screen is the face of the original Doom Guy and also makes the same faces when you punch the turkeys. First player to 3000 points wins.
Watch little movie
Once you kill the first scientist who gets turned into a zombie, look at the main control panel. One of the screens right near you should be blinking red. Click on it to watch a little movie.
