- The infamous Nightmare! difficulty wasn't in the original release of the game. People who beat it actually started complaining to Id that Ultra-Violence was It's Easy, so It Sucks for the hardest difficulty, so the devs took them up on their challenge on patches and future re-releases with a difficulty that isn't even remotely fair.
- From the ending of Doom II:
- MAP20 of Doom II, Gotcha!, becomes this in retrospect- the demons deployed their two most powerful monsters in the same spot, thinking it a foolproof plan. If Doomguy plays his cards right, they'll end up... fighting each other.
- The Xbox 360 Arcade port of Doom II has achievements that quote the Doom comic, including "You Have Huge Guts" for killing a Cyberdemon with your fists.
- In Doom 3, after you get your PDA from the receptionist, stick around and read the report he's typing on his computer. He'll eventually add a supplemental section complaining about your rudeness and how you were reading everything he typed.
- Near the end of Doom 3, long after the forces of Hell have entrenched themselves on Mars, you find a terminal with a document for you to download. The document in question? A helpful guide one of the demons wrote on how to preform a ritual sacrifice.
- During the E3 presentation of the 4th game, Doomguy comes across a palm-reader he doesn't have clearance for. He tracks down the corpse of someone who did have clearance, casually tears off his (remaining) arm and uses that to clear the way.
The tie-in comic
- The comicbook in its entirety. Special mentions go to:
- "Stupid! Stupid! Stupid Imp! You're stupid! And you're gonna be stupid and dead!"
- "Imps? Zombies? You think you can get me?!? (Thinks to himself) Wait. Maybe they don't think. (Starts yelling) Well I do! And I think you're dead! Dead! Dead! DEAD!"
- "Rip and tear! Rip and tear your guts! You are huge! That means you have HUGE GUTS! RIP AND TEAR! Oooh, here comes the night train! Choo choo CHA-BOOGIE!"
- "Knock knock who's there? ME! ME ME ME ME ME ME ME ME"
- "Aah! Chainsaw! The Great Communicator!"
- "Now I'm RADIOACTIVE! That can't be good!"
- Meta. This summary about the comic written by Doomworld.
- The EDGE review, starting with the infamous line "If only you could talk to the monsters..."
- GamePro's infamous "PRO TIP: Shoot the Cyberdemon until it dies." It's fake—the "magazine scan" is Photoshopped together—but it's funny all the same.
- The Rickroller. We would say "nuff said," but no; you've gotta see this one.
- One visual glitch is that, regardless of where on the image an enemy's weapon is, its attack emerges from its midriff. This resulted in unintended humour in the "Ultimate Simpsons" Doom mod, where the Cyberdemon is Mr. Burns... and his rockets emerge from his crotch.
- The Crafty Titan's Doom Hack... better known as Yukkuri Doom, in which everything runs on Rule of Funny and the Yukkuris are in no short supply. Oh and the rocket launcher is replaced with RAWKET LAWNCHAIR literally. https://www.youtube.com/watch?v=dske-7XjaiA part of the game in action.
- Russian Overkill gives the player intentionally game breakingly-powerful weapons, items which can casually give the player hundreds or thousands of HP in health and 100% damage reduction armor, and allows you to launch several flavors of nuclear weapon into your foes. What do they get? Health multipliers if you're feeling generous. Even the notorious nuts.wad becomes a joke with the absurdly overpowered arsenal you have available to you. Some highlights of your very extensive arsenal include:
- A character who can launch explosive, homing CRT monitors. Or drop a certain highly-explosive donkey statue.
- A character who can Sparta kick hard enough to one-shot a Cyberdemon.
- A replacement for the invulnerability sphere that makes you scream at the top of your lungs while heavy metal blares in the background.
- An automatic shotgun that can launch a spread of empty shell casings.
- An automatic shotgun that can launch a giant, bouncing shell casing that spews hundreds of normal sized shell casings in all directions to the tune of 1812 Overture.
- The most powerful weapon of all is a beacon which drops a Hindenburg-sized (and shaped) nuke that falls to the tune of Ride of the Valkyries before exploding with enough force to potentially wipe out entire maps. Even the above-mentioned nuts.wad, with over 10,000 monsters, will have upwards of 8,000 of them killed in one blast if used right.
- Naturally, the player is not immune to their own ordinance and they quickly become a greater threat to themselves than the enemies ever were.