Doom 3

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.

During gameplay, hold LEFT TRIGGER and press X, Y, B, A to become invincible.

NOTE: This code needs to be activated EVERY LEVEL for it to work. If you "exit to" and get a new area loading screen, the god mode turns itself off.

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.

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.

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.

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.

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.)

Enter your PDA, the select 'Objectives'. Hold L and press B, A, X, Y. Exit the PDA to advance to the next level.

On the Objectives Screen in the PDA, hold left trigger and press BAXY

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.