Doom

Press PAUSE while in a game. Now press and hold the # (hash) button and press PAUSE again. Release the ~ key and you'll have all the weapons, all keys and your ammo, health and armour will be totally full.

Enter one of the following codes during game play to activate the corresponding cheat function. Note: Codes may not be enabled during Co-op or Deathmatch modes.

Invincibility
Press Pause, * + Pause. Alternatively, press Pause, 9, 4, 7, 4, 9, 2, 1, 0.

All keys, weapons, full ammunition
Press Pause, # + Pause.

Fire weapons while in automap screen
Hold C + B. If the controls have been reconfigured, hold the buttons assigned to "Use" and "Fire".

Begin a multiplayer game in Level 23. Complete the level, then reset one of the Jaguars during the ending text. Start a new Deathmatch or Co-Op game on the Jaguar that was reset to play music during the next game in the place of sound effects.

Former Soldiers: They resemble your old friends, but now they just fire pistols at you. They drop clips for the chaingun and pistol when killed.

Former Sergeants: Meaner and tougher. They carry shotguns and do more damage then soldiers. They drop shotguns when killed.

Imp: This creature throws fireballs and takes more bullets to kill.

Demon: Appear in most areas and can rip your head off if you are not careful. If you see more of them, use the chaingun.

Cacodemon: These creatures are ugly and have one big mouth. If they see you, they will fire lightning balls from their mouth. Use your rockets.

Mancubus: You have to use more then a chaingun to kill them. Use ammo with caution.

Arachnotron: Fires plasma energy at you. Use your rifle.

Spider Demon: The ultimate enemy. Has a super chaingun mounted on her body. Use your plasma rifle or rocket launcher.

While in the game press PAUSE then hold down the asterix key (*) and press PAUSE again. Release the asterix key and your characters face will now have yellow eyes, indicating he is totally invulnerable.