Bathroom scare...
	Defeating Imps...
	Defeating Sarge...
	Defeating teleporting demons...
	Defeating the Guardian Of The ...
	Multiplayer information...
	Saving ammunition...
	Various Steam Achievements...

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.

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. Additionally, 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.

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.

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 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.

During multi-player mode, you can enter the console window to see if anybody tried to join. It will also show you if anybody was rejected due to an invalid password.

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 work.

Complete the indicated task to unlock the achievement.

Achievement	How to unlock
2 Deaths - 1 Gun	Kill two enemies in the same room with a rocket in DOOM 3 Multiplayer.
All of Us	Find the id logo secret room in DOOM 3.
Berserked!	Use Berserk to kill a player in DOOM 3 Multiplayer.
Big Boy	Defeat Cyberdemon boss in DOOM 3.
Boomtastic	Blow up 50 barrels in the DOOM 3, RoE, or Lost Mission campaigns.
Bot Buddy	Keep a Sentry Bot alive to its destination in DOOM 3, RoE, or Lost Mission (except Mars City).
Clean Sheet	Complete a DOOM 3 Multiplayer match without dying.
Cookie Stealer	Defeat Guardian boss in DOOM 3.
Crushed!	Catch an enemy player in the Reactor of Frag Chamber in DOOM 3 Multiplayer.
DOOM II: A Really Big Gun	Find a BFG in DOOM II single player.
DOOM II: An Important Looking Door	Find a secret area of a DOOM II level in single player.
DOOM II: And Back Again	Complete all levels in 'DOOM II: No Rest for the Living' in single player.
DOOM II: Burning Out of Control	Complete any DOOM II level with 100% kills, items, and secrets in single player.
DOOM II: From Earth to Hell	Complete all levels in 'DOOM II: Hell on Earth' in single player.
DOOM II: Just Getting Started	Complete any DOOM II level in single player.
DOOM II: Superior Firepower	Complete all 'DOOM II: Hell on Earth' levels on 'Ultra-Violence' or higher in single player.
DOOM: Burning Out of Control	Complete any DOOM level with 100% kills, items, and secrets in single player.
DOOM: Episode 1	Complete DOOM Episode 1 on 'Hurt Me Plenty' or higher in single player.
DOOM: Episode 2	Complete DOOM Episode 2 on 'Hurt Me Plenty' or higher in single player.
DOOM: Episode 3	Complete DOOM Episode 3 on 'Hurt Me Plenty' or higher in single player.
DOOM: Episode 4	Complete DOOM Episode 4 on 'Hurt Me Plenty' or higher in single player.
DOOM: Nightmare	Complete any DOOM level on 'Nightmare' in single player.
DOOM: Rampage	Complete all DOOM levels on 'Ultra-Violence' or higher in single player.
DOOMed Collector	Collect every PDA in DOOM 3.
DOOMed Marine	Complete the DOOM 3 single player campaign on Marine.
DOOMed Nightmare	Complete the DOOM 3 single player campaign on Nightmare.
DOOMed Recruit	Complete the DOOM 3 single player campaign on Recruit.
DOOMed Veteran	Complete the DOOM 3 single player campaign on Veteran.
Double the Fun!	Kill 2 Imps with one shotgun blast in DOOM 3, RoE, or Lost Mission.
Eat This!	Defeat the Maledict boss in RoE.
Evil Collector	Collect every PDA in the RoE campaign.
Evil Marine	Complete the RoE campaign on Marine.
Evil Nightmare	Complete the RoE campaign on Nightmare.
Evil Recruit	Complete the RoE campaign on Recruit.
Evil Veteran	Complete the RoE campaign on Veteran.
Fists of Fury	Use the Artifact with Berserk ability to punch out 20 enemies in RoE.
Gimme Power!	Defeat the Berserk Hunter in RoE.
Gimme Time!	Defeat the Helltime Hunter in RoE.
Goody Finder	Open all storage lockers in DOOM 3.
I Like to Watch	Find all video logs in DOOM 3.
Killing time	Score 25000 on Super Turbo Turkey Puncher 3 in DOOM 3 or RoE.
Lost Collector	Collect every PDA in the Lost Mission campaign.
Lost Marine	Complete the Lost Mission campaign on Marine.
Lost Nightmare	Complete the Lost Mission campaign on Nightmare.
Lost Recruit	Complete the Lost Mission campaign on Recruit.
Lost Veteran	Complete the Lost Mission campaign on Veteran.
Neophyte	Complete any level in Ultimate DOOM in singleplayer.
Ninja Killer	Kill 5 enemy players while using Invisibility in DOOM 3 Multiplayer.
Not a Scratch	Complete a level without taking any damage in DOOM 3, RoE, or Lost Mission (except Mars City).
Play Catch	Kill 20 enemies with projectiles launched from the Grabber in RoE.
RAGE	Find the RAGE logo in the Lost Mission.
Ready for Action!	Get the BFG-9000 from Security Chief's office in DOOM 3.
Ripped!	Use the chainsaw to kill 20 enemies in DOOM 3.
Shocking!	Defeat the Invulnerability Hunter in RoE.
Soulfood	Use the Soul Cube to defeat 20 enemies in DOOM 3.
Speed Run	Complete the DOOM 3 single player campaign in 10 hours or less.
Sticky Situation	Defeat the Vagary boss in DOOM 3.
Telefragged!	Kill an enemy player by jumping into a teleporter after them in DOOM 3 Multiplayer.
That was Close!	Kill an enemy with 1 health remaining in DOOM 3, RoE, or Lost Mission.
To Be or Not to Be	Kill the scientist trapped next to the Reactor Control Room in DOOM 3.
Too Slow, Fool!	Kill 5 enemies at once while in Hell Time in RoE.
Turncoat	Get 2 demons to fight each other in DOOM 3, RoE, or Lost Mission.
Unarmed Badass	Kill 20 enemies with the fists/melee hands in DOOM 3.
You Laugh, It Works	Find the bloody handiwork of Betruger (in Delta 4 Hallway) in DOOM 3.
You're Not My Boss!	Defeat Sabaoth boss in DOOM 3.