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"As you walk through the main entrance of the base, you hear animal-like growls echoing throughout the distant corridors. They know you're here. There's no turning back now."
The game's manual

Doom is an ultra-violent First-Person Shooter developed and published by id Software on December 1993. A follow-up to Wolfenstein 3-D, Doom was an astronomical leap forward in video game design and an even bigger step when it comes to video game violence.

Our hero is an unnamed space marine (nicknamed Doomguy) who, after putting his commanding officer in a full-body cast for ordering him to fire at innocent civilians, was assigned to the Union Aerospace Corporation base on Phobos, one of the moons of Mars. Teleportation experiments between Phobos and Deimos cause the latter to vanish and open up a portal to allow hordes of hellbound monsters to invade the Phobos base, leaving the marine as the only survivor. While searching for a way off Phobos, he instead finds himself transported to Deimos, now residing in the creatures' homeland, which turns out to be none other than Hell itself.

The release of Doom was met with unprecedented and massive controversy regarding its content. Not only was there a very high amount of explicit Satanic imagery (albeit all cast in a highly negative light), it was filled with graphic depictions of zombies and monsters being blown up, eviscerated, shot to pieces and generally disintegrating into piles of gore. People who play video games, however, would have referred to all of the above as "lots of fun for the whole family!"

Gameplay was extremely gung-ho and to the point — the developers noted that the manual could have simply read, "If it moves, kill it" — and encouraged the player to attack with reckless abandon, using such implements as a chainsaw, your own bloody fists, shotguns, machine guns and the almighty BFG, a massive weapon which could reduce entire rooms of monsters to viscera. Even the player's face, shown in between the health and armor counter, became increasingly battered and bloodied with damage like in Wolfenstein.

Also, whereas Wolfenstein's fortresses all had identical lighting and walls that were always the same height, always aligned in perfect 90º angles, and always with a minimum distance between corners or another wall, Doom featured variable lighting (including flickering and glowing lights, adding to the game's atmosphere), differing vertical heights, and walls that could be angled at any orientation and have any amount of distance to a corner or between walls (including distances too small for you or an enemy to walk through).

Another feature was the expansion of the weapons roster. Wolfenstein's weapons all behaved identically as hitscan weapons, with only the rate of fire changing. Doom's weapons would include both hitscan and projectile weapons which enemies could dodge, as well as splash damage weapons and the legendary BFG. This made the arsenal more flexible, with weapons more suited to certain situations. Enemy attacks were similarly diversified, making combat far more dynamic than it had been in Wolfenstein.

The game also introduced the idea of multiplayer death matches and co-op missions in a modern FPS, with its developers fully expecting it to be the biggest cause of decreased productivity in IT companies the world over in 1993. And they were right. It became such a smash hit that it is often credited with boosting the sales of Microsoft Windows 95, with even Bill Gates crediting it for popularizing the OS, thanks in part to his efforts to make sure there was a Win95-compatible version of the game after realizing that Doom was installed on more computers than Windows 95.

Doom built upon the formula established by Wolfenstein 3D and expanded upon it, becoming a Trope Codifier to the entire first-person shooter genre — to the point where through most of the '90s, until true 3D games really took off and started emerging from Doom's shadow, such games were often referred to as "Doom clones" as opposed to "first-person shooters". Doom's weapon selection would form the template from which many other games would base their own weapons on. The Deathmatch would become a staple of multiplayer FPS to this day. Even the game's basic premise would become a trope.

Doom was also incredibly moddable, giving birth to one of the first big video game modding communities (which first operated on BBS before migrating to the internet), which still thrives and exists to this day. Doom also played a crucial role in popularizing the idea of the speedrun, as each end-level scorecard not only keeps track of how long the player took to complete the game (alongside various completion percentages), but also included a Par time set by John Romero, encouraging players to beat it and keep finishing each level faster and faster. The ability to save runs as demo files also made sharing runs easy in an era where sharing videos over the internet was nigh-impossible. This alongside the fact that these demos record all player input and movement made Doom speedruns easy to validate for cheaters or to demonstrate speedrunning technique in an era where most games couldn't produce more proof than a picture of the game's end screen or entirely unbacked claims. The aforementioned completion percentage also allowed for tracking various categories of speedruns, such as 100% and Any%.

Doom has been ported to many, many console systems over the years. The PlayStation and Sega Saturn versions combined levels from both Doom and Doom II alongside a large number of unique missions; more original levels were released in a sequel entitled Final Doom. Doom's source code has been released, and, at this point, almost anything with a CPU in it — many cameras and music players, some watches, several appliances, and even a graphing calculator has been shown to run it for about half a minute before crashing — has had a version of Doom released for it. The common "it runs Doom" joke about fans modding the game to run on refrigerator displays, Etch-a-Sketches, or Babbage's difference engine aren't far off the mark at this point. The game also used a creepy and distinctive sound effect for doors opening, which has been re-used in many Speculative Fiction series for all sorts of things.

Long story short, Doom is one of the most influential — and infamous — games of all time.

Sequels and other media

Doom II: Hell on Earth (1994) sees the demons invading Earth. It was also a huge financial and critical success. Final Doom was released the same month as Quake; it was identical to Doom II, but came with two different Expansion Packs: TNT: Evilution, created by the third party modding group TeamTNT (originally intended to be free until id struck a publishing deal with them at the last minute); and The Plutonia Experiment, made by two members of the group in four months, generally considered the hardest of the official packs. Final Doom was also the game that included a 32-bit DirectX version of the Doom engine, making it possible to play Doom on Windows 95/98 and XP machines, besides virtual machines like DOSBox or the many source ports. It received another updated port utilizing the Unity engine by Nerve Software for PlayStation 4, Xbox One, Nintendo Switch, iOS, and Android systems in 2019, followed by a PC version in 2020 through Bethesda.net and Steam that allows players to enjoy Doom on their favorite console, handhelds, or natively on modern Windows systems with various enhancements and a selection of curated community-made mods through Bethesda.net. Its PC and iOS/Android versions also have the ability of side-loading custom vanilla-compatible and DeHackEd supported WADs. It was later re-released on GOG.com and Epic Games Store in 2022.

The third game in the series is Doom 64 for the Nintendo 64 in 1997. Running on a modified version of the Doom engine, it has the Marine returning to Mars to investigate a resurgence in demon activity. As the title suggests, it was an N64 exclusive for 23 years until a remastered port by Nightdive Studios (complete with a new epilogue campaign) was finally released for PC, PlayStation 4, Xbox One, and Switch on March 20, 2020.

A decade later, Doom³ (2004) was released. Actually the fourth instalment and also a reboot rather than a sequel, Doom 3 breaks with the first three significantly, with a dark, oppressive tone much more akin to a Survival Horror than anything. It was this incarnation on which the first movie was based. This was followed by the expansion pack Resurrection of Evil, set two years later. The game was remastered in HD, compiling the first two games with it, in addition to adding another eight levels to its campaign. Furthermore, you can actually wield a flashlight and a gun at the same time. This compilation, titled the BFG Edition, was released in October 2012. A standalone version of BFG Edition, simply titled Doom³, was developed by Panic Button and it was released along with the updated ports of the first two games in 2019.

In 2016, id Software released another game simply titled Doom (2016), a re-railing of the Doom franchise, known to most fans as Doom 4 or Doom 2016. Doom used to be known as Doom 4 when it was revealed in 2007, but the game went through Troubled Production, so id decided to revive it. The reboot is more of an Actionized Sequel compared to Doom 3, featuring faster gameplay and more emphasis on shooting rather than horror. It also purposely calls back to the gameplay of the first two titles by avoiding modern FPS mechanics like emphasis on cover, weapon reloading, and limited weapon loadouts. A sequel, Doom Eternal, was released in March 2020.

Also, a comic for Doom was made at the height of the dark age. It's hilarious, probably intentionally so. We hope. As mentioned above, there was also a movie for it, which is of debatable quality, but maintains some of the satanic imagery and violence.

There was also a series of novelizations by Dafydd ab Hugh and Brad Linaweaver. Four in all, the first two, Knee Deep in the Dead and Hell on Earth, were based on the first and second games, respectively. The final two, Infernal Sky and Endgame, went their own direction with the plot. These novels have a small cult following. There are also two novels based on Doom 3 by Matthew Costello, who also wrote that game's script.

As for other products in the franchise, there are two cell phone-based RPGs, an iOS-based Rail Shooter, and a board game with an expansion pack. For mods and fan games, see FanWorks.Doom.


This video game provides examples of:

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  • 12-Bar Blues: A large number of songs use this chord progression in some form, most famously At Doom's Gate (E1M1). On The Hunt (E1M6) also uses it, while The Imp's Song (E1M2) uses a slower, corrupted version of it.
  • 100% Completion: Each level ends with percentage counters for how many monsters were killed, items collected, and secrets found. Some source ports will reward you with a "Perfect" rating if you get 100% in all three categories.
  • Acceptable Breaks from Reality: As you may recover shotgun shells and even their Shotguns from them, there's no logical reason why Sergeants fire only three shotgun pellets instead of seven like you can. However, this would make Sergeants into very dangerous and potentially frustrating enemies, so their firepower was reduced.
  • Acid Pool: Starting from the first level (E1M1), the game features wide pools of green acid that inflict gradual damage onto Doomguy upon contact, though none of them are deep enough to make him sink (in fact, he can still walk and run over them). There are lab coats that give Doomguy full protection against them, but only for a limited time.
  • Advanced Movement Technique: This game and its sequel share a common speedrunning tactic known as straferunning. When you run diagonally, depending on what keys you are holding, you can achieve a speed that is either 28% or 41% faster than normal running speed. This not only makes regular transit significantly faster, but depending on the map, can even allow minor/major skips via Sequence Breaking.
  • After the End: The game's story takes place with nearly every other human dead before you even start moving.
  • Airborne Mook:
    • Cacodemons are floating, cyclopean masses of flesh that shoot projectiles and can take a fair amount of damage before being defeated.
    • Lost Souls are floating skulls in flames that attack Doomguy by dashing towards him.
  • Alien Blood: The Cacodemons and Barons of Hell appear to leak blue and green fluids when they die, even though their blood spatter when hit while alive uses the same red color as seen for other creatures in the game. The developers say this is because both do have red blood, but their innards are blue/green. However, it has been suggested that they simply didn't have a way to color-shift the red blood splatter sprites and did not want to waste space on differently-colored graphics. Some modern source ports have remedied this by allowing the blood color to be shifted for different enemies.
  • Alien Sky: The game features several variations on a red sky for Fire and Brimstone Hell, made more noticeable when Doomguy gets into Hell in the third episode.
  • All There in the Manual:
    • The manual gives the backstory for the game in fairly elaborate detail. The ending text of Episode 1 even seems to assume that you've read it, making reference to "the missing Deimos base" without further explanation, which would only make sense if you read the synopsis.
    • Also, the novelizations are the only time "Doomguy" is given a proper name (for those wondering, it's Flynn "Fly" Taggart for the classic series novels). The developers stated that the game's protagonist is deliberately not given a name because it's supposed to be you, the player.
  • Always Chaotic Evil: The demons all have nothing but malicious intent towards everyone and everything around them - even other demons if one of them hits another.
  • Ammunition Backpack: As a power-up. Not only does it give you one of each "small ammo pack" (one pistol magazine, four shotgun shells, one rocket, and one 20-volt energy cell), if it's your first, it doubles your ammo-carrying capacity (you can carry 400 bullets and 100 shells instead of 200 and 50, and so on).
  • And I Must Scream:
    • Some crushing floors in the first two games only crush, they never release. If you let yourself be smashed by these and happen to have enough health, you'll remain trapped alive in concrete. Have a nice stay if it's multiplayer and no one else can find and kill you to release you. Thankfully, a rather rare bug.
    • One rare wall texture is simply just faces melted together and apparently in agony.
  • And Your Little Dog, Too!: At the end of the third episode, Doomguy returns to Earth only to find the cities burning and a rabbit with its head speared on a stake. In the extra chapter, Thy Flesh Consumed, it's revealed that this rabbit was Daisy, Doomguy's pet rabbit.
  • Anti-Frustration Features:
    • In the original games, the highest and lowest difficulties both doubled ammo. In the case of the latter, it's an obvious "make it easier by letting the player spam stronger guns", but in the case of the former, you'll need the double ammo drops to handle the increased quantity of eternally respawning enemies.
    • The game normally switches weapons automatically if you're out of ammo for your current one (such as switching from the chaingun to shotgun if you are out of bullets but still have shells). However, the game will never switch you to the rocket launcher (even if the only other weapon available is the fist), as it would be way too easy to blow yourself up if this happened in the middle of a pitched battle.
    • Lost Souls do not count as kills when the end-level screen calculates the percentage of enemies you have killed, backporting a bit of behavior from Doom II that was most likely a concession to the fact that Lost Souls have a nasty habit of clipping out of bounds in the second game when they are spawned by the death of a Pain Elemental. This solution means that your 100% run doesn't become Unintentionally Unwinnable due to an unlucky Lost Soul disappearance.
  • Armor Meter: You have separate armour and hit-point tracks. Armour absorbs a set percentage of hit point damage depending on its colour: 33% for green armour and 50% for blue. Counterintuitively, this means collecting green armour within a certain range of values can actually make you more vulnerable.
  • Armor Points: Doomguy's armor provides a better defence against melee attacks and projectiles when armor points are collected in the levels. There are powerups that can raise the cap, though they cannot be replenished once they're spent by taking damage and reducing their current amount to under the original cap will also undo the extension.
  • Arrange Mode:
    • In the Harder Than Hard "Nightmare!" difficulty, monster projectiles are faster, Pinky demons move faster, and enemies respawn several seconds after death. Oh, and you can't use cheat codes. You also receive the same doubled ammo bonus as in the "I'm Too Young To Die!" difficulty. You'll need it.
    • The 2019 Unity ports added an "Ultra-Violence+" difficulty in between Ultra-Violence and Nightmare!, which features faster enemies and weapons available from the multiplayer modes without the respawning monsters from Nightmare! mode.
  • The Artifact:
    • One of the computer screens in the starbase texture set contains the words "Tei Tenga", which was the name of the originally intended setting of the game in Tom Hall's Doom Bible before Hall departed the project and the action was moved to Mars' moons.
    • The Ultimate Doom, the 1995 rerelease which modern ports of the game are based upon, retained the ending text of "The Shores of Hell" that refers to episode 3, "Inferno", as the final episode, as well as the ending to "Inferno" itself that features a big "THE END" appearing on screen, even though that version also added a fourth episode.
    • Most console ports copy the original PC heads-up display precisely, including the "ARMS" display, which is numbered "2" through "7" to represent which number key can be pressed to pull up which weapon, even though console controllers - excluding the Atari Jaguar, the one version to get a Doom port actually made by the original developers - don't have number pads.
    • The early console ports have several other artifacts due to somewhat delayed development, as they were based on code from v1.2 but only released by the time Doom II had been released on PC and the original game had been updated to v1.7, so they lack some gameplay elements or minor changes to the maps made with later versions.
    • The Playstation and Saturn ports used the Jaguar port as a base, with the maps that were in the Jaguar port being unchanged aside from modifying the lighting, thing placement, and fixing a few bugs. As a result, their Episode 1-3 maps are cut down a lot more than they needed to be on these more advanced consoles, which compare in stark contrast to the Episode 4 and Doom II maps newly added to these ports that are closer to their PC counterparts despite being generally more complex maps. Those maps from Jaguar Doom are additionally missing any crushers and teleporting monster traps they originally had despite the ports being able to handle them (and indeed they're still present in all the other maps that weren't copied from Jaguar Doom).
  • Artificial Stupidity:
    • It doesn't matter if a fellow monster is in the way, all monsters will start attacking upon sight of the player, and if their attack connects with a fellow monster, they'll turn on each other. Players who are out of ammo will quickly learn to start triggering in-fights. The term "monster infighting" was coined to describe this (especially when other games began featuring the same thing).
    • Pinkies will always charge straight at the player, regardless of what's in their way. If you've got the chainsaw, all you have to do is hold down the fire button and they'll happily charge right into your blade and get torn apart.
  • Artistic License – Arachnids: The Spider Mastermind and her Arachnotrons (not seen until Doom II and onward) all have two vestigial arms and four mechanical legs. Granted, they're just demons with "spider" in their name.
  • Artistic License – Medicine: Somehow Doomguy can use as many stimpacks and medkits as he wants without overdosing on all the stimulants and narcotics that must be in his system.
  • Artistic License – Nuclear Physics: The game tends to have open pools of radioactive waste as a type of hurt floor, typically shown as being slightly less dangerous than lava. The toxic waste is called nukage and is stored in Exploding Barrel drums; the game's booklet describes the damaging floors as "slime and other radioactive waste". There are radioactive warning signs, while the radiation shielding suit, Toxin Refinery, and Nuclear Plant maps suggest Union Aerospace Corporation was operating a nuclear power plant and waste handling facility on Phobos.
  • Artistic License – Space: The original Doom takes place on Mars' moons, Phobos in episode 1 and Deimos in episode 2, which are depicted as having Earthlike gravity and atmospheres. In reality, Phobos and Deimos are tiny moonlets no more than 20 kilometres across, have gravity so low you could probably jump into space off them, and have no atmosphere (and even if you could artificially generate one, the gravity of the moons would not be enough to keep it from floating away).
  • Ascended Glitch:
    • The shimmery "hall of mirrors" effect that occurs when a texture is missing has been adopted by some level designers to create deep water. It will still glitch if your view is below the water level, however.
    • Also the "voodoo doll" bug, which can be easily created by placing two different start points for a single player. Clever mapmakers have used this bug to create traps that can teleport a player into another copy of himself, resulting in a recursive Tele-Frag (MAP30 of TNT: Evilution is an example). Voodoo dolls under triggered crushing ceilings can also be used to cause player deaths wherever the mapmaker wants; for example, simulating bottomless pits by triggering the ceiling if a player falls into one, or giving a time limit by having a descending ceiling which will eventually crush the voodoo doll.
    • It is possible to mess with sectors and sector references to create an "invisible staircase" effect, which was first demonstrated by a map called UAC_Dead.wad. This in fact abuses the same glitch as the deep water effect above, just the water doesn't need some of the set-up needed for bridges.
    • If you trigger an action to move the floor up, but the target height is lower than the current height, then the floor will move instantly (and the other way round, if the floor should be moving down but the target height is higher, it will also move instantly). Combined with the "invisible bridge" effect above, this allows for a fake 3D bridge that can be passed over and under, by moving the floor depending on where the player is. This is used in some custom maps. It is also used heavily in Doom 64 to create bridges and tunnels.
    • Under the right circumstances, it's possible to finish a level while (or even after) dying, causing you to start the next map with the standard 100 health, no armor, and only a pistol with 50 bullets. Map makers have exploited this by designing their map exits in a way that forces the player to die while triggering them to induce a Bag of Spilling (known by the community as "death exits"), whether to emulate the first Doom's episodic structure in Doom 2, to create a No-Gear Level midway into their megawad, or simply to force the player to Pistol-Start each map of their WAD.
  • As the Good Book Says...: The entirety of "Thy Flesh Consumed" and eight of its nine levels have titles that are referenced from the King James version of The Bible:
    • "Hell Beneath" is taken from Proverbs 15:24.
    • "Perfect Hatred" and "Against Thee Wickedly" are taken from the verses of Psalm 139, verses 20 and 22.
    • "Sever the Wicked" is taken from Matthew 13:49, which is an excerpt from the Parable of the Fishing Net (13:47-50).
    • "Unruly Evil" is taken from James 3:8.
    • "They Will Repent" is taken from Luke 16:30, which is also an excerpt from the Parable of the Rich Man and Lazarus (Luke 16:19-31).
    • "And Hell Followed" is taken from the Book of Revelation, Chapter 6, verse 8.note 
    • The episode title itself ("Thy Flesh Consumed") and that of its final mission ("Unto the Cruel") are taken from the two verses of Proverbs 5, verses 9 and 11, respectively.note 
  • A-Team Firing: Normally, monsters fire directly at the player, allowing the player to dodge. If you collect the Partial Invisibility power-up, enemies will fire wildly in your general direction (and miss more often than not). Ironically, this can actually make it harder to avoid getting hit sometimes if you pick up a bad habit of dodging projectiles or if there are a lot of enemies in an area because you can accidentally dodge into one of the stray ones; most custom maps use the sphere for this purpose, by forcing you to collect one before entering a large battle with a lot of demons. However, the powerup is surprisingly good when dealing with hitscan enemies, since you can't dodge their bullets and Partial Invisibility will mess up the RNG and make them miss almost all the time, saving you a lot of pain.
  • Attract Mode: The game will play a demo if left on the title screen for a second or two.
  • Autobots, Rock Out!: The first game and Doom II both use generic MIDI versions of heavy metal songs for their music. John Romero is quoted as saying that the games' composer Bobby Prince "knew the legal amount of sampling that he could do without getting into trouble." This page on the Doom wiki details the various inspirations for the music; for instance, the famous riff from E1M1 was taken from Metallica's Master of Puppets.
  • Auto-Save: Many source ports, such as ZDoom or Zandronum, auto-save whenever the player enters a new level, whilst also having the option of manual saves.
  • Awesome, but Impractical: The Berserk pack. It brings you back up to 100 health if you're anywhere below that, which is a godsend if you're down to 10 or 20 health. On top of that, as its name implies, it boosts the power of your punches for the rest of the level to the point you can gib zombies and imps with one or two hits. But why would you risk rushing into a horde of enemies to punch them to death one at a time while the others tear you to shreds? It's mostly good for ammo-crunch situations.
  • Back from the Brink: The game has the protagonist fighting off a demonic invasion after all his comrades on the Phobos base are wiped out.
  • Back That Light Up:
    • The Game Boy Advance version of Doom had more than one color scheme to compensate for the different lighting possibilities for that system.
    • An early patch added several "gamma correction" settings to lighten the game, to help compensate for the terrible backlighting of CRT monitors commonplace at the time.
  • Badass Normal: The marine. Even the manual outright calls him the "toughest space trooper ever to suck vacuum."
  • Bag of Holding: The backpack is a collectible that doubles the ammo you can carry.
  • Bag of Spilling: The game is divided into three (later four) episodes, each of which starts you off with only your most basic weaponry; while there's an excuse for one episode (you end episode 1 by getting killed, and start episode 2 in Hell), the others don't bother.
  • BFG: Not just any BFG, either, but the BFG. The BFG9000 is a gigantic monster of a weapon, which consumes 40 energy cells per shot to fire a massive orb of plasma that will vaporize most demons in the room with a single blast.
  • Big Labyrinthine Building: Almost an uber-example of this trope, with many levels taking place in gargantuan buildings.
  • Big Red Devil: The Barons of Hell evoke this the most, looking like satyrs with pinkish-red torsos. With different colorations, the Cyberdemon and Hell Knight are pretty close to this trope as well.
  • Black-and-White Morality: All the Doom games, really. Monsters from Hell trash humanity For the Evulz. You have lots of guns. Monsters goo-ify quite nicely. There's not a lot of ambiguity when it comes to what you're supposed to do.
  • Black Blood: Enemies bleed green in the Game Boy Advance ports of Doom and Doom II.
  • Blackout Basement: The games have a fair share of darker levels. Spectres tend to lurk around these in larger numbers than usual, and sometimes, you may just find a Light Amplification Visor. In the worst offenders, it's easier to navigate by looking at the automap. Particular standouts in the first game are the penultimate room of E1M5, "Phobos Lab", and the southwestern portion of E2M6, "Halls of the Damned".
  • Blatant Item Placement: In Doom/Doom II, it's rare that item collection triggers an ambush or trap, but some do exist. However, some items are shown on display (e.g. the armor in E1M1) for no reason.
  • Blood from the Mouth: The marine's portrait whenever his health is low enough.
  • Bloody Bowels of Hell: A lot of the "hell" levels of the original Doom and Doom II. Walls of skin that's sometimes wounded or peeling off and floors made out of intestines are commonplace, at least one room has walls made out of large numbers of corpses compacted together, and boiling blood is a common type of hazardous floor.
  • Bloody Smile: The Space Marine's mug is in the centre of the status bar. As he takes damage, his head gets more dishevelled and bloodier. Lower than 40% health will cause bleeding in his mouth, visible when he picks up a new weapon, smiling at his increased killing power. It hurts less making hellspawn hurt more.
  • Body Horror: The original Doom games have plenty of walls in the hell levels appearing to be made of human flesh, faces, or piles of corpses.
  • Bolivian Army Ending: At the end of the first episode, the protagonist winds up in a room filled with acid and surrounded by quite a number of demons. As his health quickly drains away, the game ends. For the Shareware version, this was a cliffhanger of sorts.
  • Border-Occupying Decorations:
    • The 3DO version always has a brown border around the action. This is done not due to gameplay not taking up enough space, but because the port's quality results in the game lagging at larger screen sizes. The two highest options have to be enabled with a cheat code, and even the largest has some brown on the sides.
    • The 2019 Unity ports of the first two games used border art based on the intermission screens of the No Rest of the Living expansion to fill the unused space on the sides, although the game's aspect ratio was incorrectly scaled which resulted in a stretched image. Later patches fixed the aspect ratio while keeping the border art up until September 3, 2020 update that implemented an official 16:9 widescreen presentation with the option of the original 4:3 display, however, the game's used unused space is filled with the background image of the game's IWAD similarly to the DOS version.
  • Boring, but Practical:
    • Your trusty ol' shotgun. It does pack a decent punch, especially up close to an enemy. And ammo for it is relatively quite plentiful compared to the more exotic weaponry like the plasma gun or BFG. Also, due to its rather decent amount of damage output, the shotgun is also pretty good at dealing with most common enemies.
    • The Backpack powerup. A single backpack doubles your ammo capacity when you pick it up for the first time. This allows you to (obviously) carry more ammo so you don't run out during intense firefights and have to retreat to find more. Also, the Backpack gives you a small amount of ammo for every weapon (even for ones you don't have yet). While the double ammo capacity perk only happens once (until you die or do a "pistol restart"), the ammo boost for every weapon is always welcome.
  • Boss Corridor: The levels E1M8 ("Phobos Anomaly") and E3M8 ("Dis") both take this form; the former precedes the Dual Boss fight against two Barons of Hell (the only ones to appear in the game's first episode, and the first ones overall), while the latter precedes the Spider Mastermind.
  • Boss in Mook Clothing: Barons of Hell are just plain tough with 1000 hitpoints, so killing one with anything weaker than the rocket launcher is a prolonged waste of ammo, and where there's one Baron, there are likely more.
  • Boss-Only Level: The endings of episodes 2 and 3, respectively Tower of Babel (a fight against the Cyberdemon) and Dis (Spider Mastermind), at least on lower difficulties (higher ones add a couple of Lost Souls to the former and Cacodemons and a Baron of Hell to the latter).
  • Boss Room:
    • The secret level for Episode 3 looks exactly like the map for that episode's Mission 1 until you get to the end of the level, and step on what you think is the exit teleporter. A wall drops instead, exposing a Cyberdemon (the really tough boss of Episode 2, who is also fought in a similar area), and the key card you need to acquire is behind him, so you either have to kill him or run well enough to get past him, steal the key and leave.
    • The eighth mission of each episode features a boss battle: Two Barons of Hell in the first, Cyberdemon in the second, and the Spider Mastermind in the third and fourth (though the latter is much more elaborate, thus not being a Boss-Only Level).
  • Bottomless Magazines: Downplayed; you have a finite amount of ammunition for every weapon, but you never have to reload, beyond pumping the shotgun between each shot.
  • Bowdlerise:
    • Swastikas in E1M4 in Doom were changed in later versions to allow the game to be sold in Germany.
    • The Game Boy Advance ports of Doom I and II had all the in-game blood turned green — which had the side effect of turning objects such as shotgun shells, pipes on walls and other items green as well, since they merely changed the base palette. Enemies no longer explode into bloody chunks as well, resulting in these ports getting a Teen Rating by the ESRB. Ironically, the SNES port of Doom retained most of the original game's red-blooded violence, with only the Satanic symbols being censored.
    • In the 2019 Unity ports of Doom, its version of REKKR features Valkyrie statues that were originally nude but were changed to be clad in armor instead. However, according to one of the mod's authors, he doesn't mind this change and prefers the armored version.
  • Brain Monster: The final boss of the third and fourth episodes — the Spider Mastermind — is essentially a giant brain carried by a robot body.
  • Brutal Bonus Level:
    • Episode I's Military Base. Coming right after three fairly easy levels even at higher difficulty settings, this is a serious challenge for beginners. A large number of monsters, tight, closed areas, a number of nasty traps with enemies suddenly teleporting out of nowhere, lots of close-quarter combat, barely-visible Spectres looming in the dark and suddenly ambushing you - if you have just started with Doom, surviving Military Base is a heavy challenge.
    • Episode II's secret level, Fortress Of Mystery. You begin the game in the centre of a compact, 8-part flower-like structure, instantly greeted by four Barons Of Hell charging and firing at you from all directions. Manoeuvering is tricky because the "petals" have narrow entrances and it's easy to get cornered by the Barons if you try to run. Hopefully, one of the "petals" ends in a door, so you run there and open it, hoping for a refuge... then you hear a hiss of ten Cacodemons just waiting for you in a mid-sized room. The level is actually fairly easy when you know the trick to it (namely, tricking both groups of powerful monsters into infighting and trying to stay the hell away until only a few remain), but considering the player never meets that many heavy opponents in a tightly enclosed space at once in the original Doom (Ep III's Mt. Erebus has its clusters of Cacodemons, but you battle them in an open space and there are much fewer Cacos on lower difficulty levels, while the number of enemies in Fortress is the same regardless of level) and the BFG is not available at all until Episode III, it was a serious spike in difficulty from the previous levels of the game.
  • Bullet Hell: The game (and any of its sequels) can become this if you meet too many enemies at once, in particular on Nightmare! difficulty, which speeds up enemy projectiles and causes enemies to respawn on death. Even outside of Nightmare! difficulty, there are enemies that are happy to shoot you on sight, including homing missiles courtesy of the Revenants, and hitscan enemies whose attacks you can't even dodge.
  • Bunnies for Cuteness: Used for humorous effect in the episode "Thy Flesh Consumed". The finale of the original campaign saw Doomguy heading home to Earth to find it overrun by demons. As if the invasion itself wasn't bad enough, they even killed his pet rabbit Daisy and stuck her head on a spike. And if you thought Doomguy was mad at the demons before...
  • Canon Welding: The cell phone RPGs are in the same continuity as Wolfenstein RPG, which features the "Harbinger of Doom" as the final boss. The Harbinger gets his arm and leg blown off and swears to avenge himself on B.J.'s descendants, becoming the Cyberdemon.
  • Cap: The game's engine can support custom monsters with a maximum HP of 2,147,483,647. The strongest boss in the vanilla game has 4000, so two billion should be enough for even the most masochistic creator.
  • Cap Raiser: The Backpack doubles the amount of ammo that you can carry for all of your weapons.
  • Cephalothorax:
    • The Cacodemons are floating monster heads that shoot things at you.
    • The Spiderdemon takes the form of a giant brain with a face on the front and tiny spindly arms carried about on a multi-legged combat chassis.
    • Pain Elementals were added in Doom II, and they have the addition of two small arms on the side.
  • Chainsaw Good: The chainsaw replaces your fists as the Emergency Weapon once you find it, works like a melee-range chaingun and works quite well as a way to save ammo when dealing with lesser enemies. The weapon proved so popular in the original game that it's the first available weapon in the sequel, so long as you remember to look behind you. That said, in high-level play, it's very unfavored by players due to two characteristics: one, it pulls the player into the monster he's sawing, jerking his aim every which way; two, the blockmap bug from the original games and preserved in the more faithful source ports makes hitboxes unreliable for hitscan attacks, which melee counts as.
  • Charles Atlas Superpower: All that is required to literally fight your way to Hell and back is to have trained at boot camp. The story goes that Doomguy was apparently a very competent trooper, who got reassigned to Mars as a grunt after punching out a superior officer when given a direct order to fire on innocent civilians. Of course, shortly after he arrived, shit hit the fan. In the first novel, he gets the hell beat out of him a lot and has a lot of trouble going on. Thank goodness for the in-canon magical healing balls of creepy. And if you believe the comic, Doomguy was quite unhinged and seemed likely to be the kind of guy who you'd expect to be able to survive a trip to hell and back just because of his sheer lack of a grip on reality. Whether or not this came before or as a result of the Hell invasion is open to interpretation, however.
  • Cherry Tapping: The bosses have many hit points, hit for massive damage and of course have predictable patterns that enable a player to kill them without getting hurt. As a result, there are a number of videos showing someone killing a Cyberdemon or Spider Mastermind with a lowly pistol or even fists.
  • Chuck Cunningham Syndrome: The Yorps, Gargs, and other aliens living on Mars in the Commander Keen series are inexplicably absent from Doom and all of its follow-ups, despite the fact that both series share a universe. But at least the original series excused this absence by having none of the games actually take place on Mars itself. Besides, having cute little alien critters running around would've probably clashed with the Darker and Edgier tone of Doom.
  • Classic Cheat Code: There's a number of cheat codes prefixed by the character sequence "ID" — the most popular being "IDDQD" (God Mode) and "IDKFA" (full armor and ammo plus all weapons and keys). The "ID" prefix obviously stands for developer id Software, but not many fans know that "DQD" stands for Delta-Q-Delta, the name of a three-person informal fraternity organized by Doom programmer Dave Tailor during his college days ("Degreelessness Mode" refers to their habit of dropping courses they were failing to receive an "Incomplete" grade, while the "-ness" suffix was part of id's in-house slang). "KFA" simply stands for Keys, Full Ammo.note  Several later games, particularly in the same genre, have carried on the tradition.
  • Cliffhanger: The ending of Episode I has the marine finding himself teleported into a dark room with a damaging floor, surrounded on all sides by enemies, and unable to escape. The episode ends just as he's down to his last health points. Episode II begins with him alive and well. According to the developers, the marine killed all the enemies and escaped.
  • Climax Boss: The Cyberdemon is the boss of the second episode out of three. It was even featured on the sequel's cover!
  • Clothing Damage: As seen in the page image, Doomguy's uniform is heavily damaged in most official artwork. Amusingly, this led to some players thinking that his armor was issued with an abdominal cutout. (if you zoom in close on the guy in the background you can see that his midriff is covered, while there are ragged edges on the central marine's hole where the armour was ripped away).
  • Color-Coded Multiplayer: The first game's multiplayer has each player a different color. One of the colors is brown, and this mixed with the old-school graphics and brown-colored enemies can cause problems.
  • The Colored Cross: The original releases of Doom and its earlier console ports featured a red cross for the stimpacks, medikits, and berserk power-up. In the 2012 Xbox 360, PlayStation 3, and BFG Edition ports of the first two Doom games, the Red Cross was replaced with a red-and-white pill. The 2019 Unity ports later replaced the pill icons with a green cross instead.
  • Combinatorial Explosion: Touched on in the first novel. The characters want to use a rocket launcher on the red-key door, but it's structured such that it'll take all their ammo to do it. They decide to get the red key anyway in case they need to save the rocket ammo for something horrible, even if that something horrible (a Hell Prince) might pop up and take all their rockets to kill while they're looking for the red key.
  • Compilation Rerelease: The classic series has been included in a few compilations across PC and other platforms.
    • The id Anthology not only compiles of all the classic Doom games, it also includes Wolfenstein 3-D, Quake, and the entire Commander Keen series across four CD-ROMs. This collection also added some bug fixes to TNT: Evilution and The Plutonia Experiment, and this version serves as the basis of the GOG.com release and the downloadable add-ons for the Unity ports.
    • The Depths of Doom Trilogy is a PC compilation that included The Ultimate Doom, Doom II, and Master Levels for Doom II across three CDs, along with the shareware version of Heretic, an amateur set of levels called Maximum Doom, and DWANGO version 2.02 for multiplayer at the time.
    • Doom: Collector's Edition for PC includes The Ultimate Doom, Doom II, and Final Doom on a single disc. It also allows players to play the classic Doom games without using virtual machines such as DOSBox or source ports.
    • The BFG Edition includes Doom and Doom II, albeit the Xbox LIVE Arcade ports that have various alterations including the censored versions of the Wolfenstein 3D secret levels in Doom II... on the plus side, it gives PC players a chance to officially play the Doom II XBLA-exclusive episode "No Rest For the Living". In November 2012, the PlayStation 3 received another compilation called Doom Classic Complete, which includes the original two games plus "No Rest for the Living", as well as Master Levels for Doom II and Final Doom, marking the first time in a long while that TNT Evilution and The Plutonia Experiment have been seen on home consoles.
  • The Computer Is a Cheating Bastard:
    • A combination of Fake Difficulty and bastard map designers, it does not matter how carefully a player clears rooms and watches dark corners as there will always be tiny, function-less, hidden, and effectively invisible closets containing idle monsters whose sole purpose is to surprise the player from behind.
    • To a lesser extent, there's the way hitscan enemies (riflemen, shotgunners, spiderdemons, etc) can pseudo-randomly aimbot you at any range, even if they're a single pixel on a distant mountain. While this doesn't matter much in the enclosed spaces of the base game, in some custom levels favoring open spaces, this can get very annoying.
  • Container Maze: The first room of E2M2: Containment Area in the first Doom is basically a maze of crates with UAC supplies.
  • Continuity Reboot: Happened twice. Doom 3 and its expansion Resurrection of Evil does not descend from the events of Doom and Hell on Earth and the 2016 game is another reboot that does not follow on from 3. Eternal subverts this by revealing that it and 2016 are Stealth Sequels. It also implies 3 fits in somewhere.
  • Contractual Boss Immunity: Cyberdemons and Spider Masterminds are immune to splash damage. They only take damage from the rocket itself, not the explosion.
  • Convection, Schmonvection: Doom is all over the place with this trope. Part of the issue is the way the game handles floor types: what the floor is made of and whether or not it damages you (and by how much) are stored separately for each section of floor, meaning some levels have lava that doesn't harm you at all, others where some other variety of liquid (typically blood) harms you just the same as lava, and others still where lava in one location won't harm you, but past some arbitrary section of the pool will suddenly damage you. Even for levels that have regular damaging lava, the lava only damages you if you wade in it for more than a full second. And when you add on the ability to jump introduced in several source ports such as ZDoom, you can even wade through the lava far longer than normal with minimized damage by splashing up and down in it. This is par for the course in Hell, which is supposed to be full of fire that burns but doesn't consume. However, for levels that take place on Phobos, Earth, or Io there's no excuse.
  • Covers Always Lie: The cover of the first game shows the Marine wielding what seems to be some kind of submachine gun or small assault rifle, despite the game having no such weapon. It did, however, exist in the alpha — but that weapon was turned into a chaingun during development. It eventually made its way into Doom³, albeit with a redesigned appearance.
  • Crate Expectations: About two-fifths of Episode 2 Map 2 is a maze made of crates. And if you abuse the Doom engine, you can go Crate-Jesus and run along the tops of them as if they were side by side. The multiplayer source port Skulltag has a skin that is a crate.
  • Creator In-Joke:
  • Cruel Twist Ending: Twice over: the ending of the first episode suggests that Doomguy has won by clearing out the demons on Phobos, only for him to be ambushed in an inescapable room and actually killed by the demons. The third episode, once he's fought his way through Deimos and Hell itself to make it back to Earth, suggests that everything will be fine once he's back, only for it to turn out that the demons have already invaded Earth. And they killed his pet rabbit, Daisy.
  • Curb-Stomp Battle:
    • The ending of the first episode ambushes the player after they take the exit teleporter, with high-damage enemies attacking from all sides, along with being on a floor with the highest damage-per-second.
    • The final weapon, the BFG 9000, deals 3150 average damage (and, due to 601 dice rolls being done, very little deviation from that). The Spider Mastermind, in comparison, has 3000 health. This means the final boss of Doom can be slaughtered in a single shot with a weapon you find on the third map of the third episode (keep in mind there are nine maps, the ninth's secret, and it's on every map afterwards save the eighth).
  • Cut and Paste Environments: The game takes advantage of this for the secret level of its third episode. When you enter it, by all means, it appears to be an exact copy of the first level of the episode, up until you hit the original exit switch and the walls lower to reveal an open area with a Cyberdemon. You then have to go back through to the start of the level, with walls lowered to reveal new monsters in every room, to find a new hallway in the beginning room leading to the key to exit the level.
  • Cycle of Hurting:
    • A crucial mechanic of Doom is that each time an enemy is hit, they may enter what is called a "pain state", where they're stunned for a split-second, disrupting their attack and movement. With rapid-fire weapons, enemies can have their pain state repeatedly triggered, keeping them from attacking nor moving until they're dead. The higher the enemy's pain chance, the more vulnerable they are to this.
    • The player doesn't have a pain state like the monsters and so can never be stunned when hit. However, there's a different mechanic for the player where whenever they're hit, their screen will flash red, with the intensity of the redness being determined by the amount of damage they took, and successive hits while the player is still recovering from the prior hit will build the intensity too. If the player takes a particularly nasty hit, like a direct hit from a Cyberdemon rocket, or is hit by many attacks in quick succession, such as being shredded by multiple Chaingunners, the entire screen can become completely red and effectively blind the player for a couple seconds - making it all the more likely they'll get hit even more as they blindly try to scramble to safety.

    D-E 
  • Damage Discrimination: With the exception of bullets, monsters are immune to their own kind's projectile attacks.
  • Damage-Sponge Boss:
    • The Barons of Hell (the first two of which are introduced as bosses, a.k.a. the 'Bruiser Brothers', at the end of the first episode) are considered to have hit points well out of proportion with their actual threat level. This led to the introduction of Hell Knights in Doom II, which were about as dangerous (their plasma orbs and claw attacks did the same damage), but only half as tough, making them slightly closer to a Glass Cannon that could be placed more often without needlessly slowing down the pace of combat.
    • The Cyberdemon takes a lot of hitsnote , shoots rockets which can one-shot you with a direct hit at 100% health, and is defeated by circle strafing and shooting. It led to the creation of the sarcastic "tip" of "To defeat the Cyberdemon, shoot at it until it dies." The same goes for every other boss in the original Doom games, including the Barons of Hell and the Spider Mastermind. There's another complication regarding the Cyberdemon in the first Doom game. When you first encounter him, the level there has a huge supply of ammo for your Rocket Launcher, which is (at that point in the game) the weapon with the most raw power. The problem is that the Cyberdemon is immune to splash damage, meaning that only the damage caused by the direct hit has any effect on him. If you opt to use the rocket launcher, the battle ends up being drawn out even longer. If you have a surplus of cells, it's far faster to whip out the Plasma Rifle instead. Thankfully when he appears again in the secret level of episode 3, you might've finally found the BFG, which makes the rematch a lot easier.
    • With the Spider Mastermind, which has 3000 HP, the fact that its Triple Chaingun is a hitscan weapon does require you to put a little thought into not getting killed. But still, that only changes the strategy to "Shoot it until it dies, and don't wind up full of hot lead."
  • Darker and Edgier: The PlayStation and Saturn versions of Doom introduced darker music, colored lighting to give the levels a more foreboding feel, and revoicing the demons to appear far more intimidating.
  • Dark Is Not Evil: Your Space Marine character has some pretty strong Blood Knight qualities (just look at his diabolical grin when he picks up a new weapon), and he wound up stationed on Mars due to a violent case of insubordination. His offence, by the way, was putting his C.O. in a body cast for ordering their squad to fire on civilians.
  • Dead Character Walking: Has such a bug, described in detail here, where a player killed in deathmatch becomes a mobile corpse which runs (okay, slides) around. Kinda creepy.
  • Deadly Dodging: Luring enemies into firing at each other and then fighting is an essential combat tactic, especially when up against maps with tons of enemies and not enough ammo to kill them all yourself.
  • Dead Guy on Display:
    • The demons really like hanging their victims from the walls and ceilings. The reason for this isn't explained, but most likely it is to scare off intruders (i.e. you) and/or as snacks for later.
    • And then there's what they do to Doomguy's poor little bunny at the end of the first game, killing it and mounting its head on a spike as they invade Earth.
  • Deadly Dodging: A major tactic is to slip between enemies (or at least ensure one is between your attacker). If one enemy damages another with a ranged attack or barrel explosion, this results in monster in-fighting (generally resulting in one of the enemies dying.)
  • Degraded Boss:
    • Two Barons of Hell serve as the Dual Boss concluding the first episode. More of them appear in the subsequent episodes and later sequels as normal (but still powerful) enemies.
    • The Cyberdemon debuts as the boss of the second episode then reappears as a Boss in Mook Clothing in the secret level of the third episode and the second level of the fourth; it's then promoted back to being the boss of the fourth episode's sixth level. The Spider Mastermind, while being degraded in the second game, averts the trope here for being the Final Boss of both Episodes 3 and 4.
  • Deliberately Monochrome: The invincibility powerup turns everything black and white while active, most likely so it's obvious when it wears off.
  • Dem Bones: The Lost Souls, which are floating flaming skulls.
  • Descending Ceiling: There are two versions, both doing the same damage over time. The "slow" descending traps the player by slowing down the crushing process, while the fast one does a quick crush and raise. Also, during the crushing phase, the player can't move because the ceiling is too low. Both of these are introduced in E2M4, the "slow" crusher having blood splatters on the ground, while the fast crusher is a surprise trap covering the key.
  • Devil, but No God: It seems the only force of Good in the verse is our hero Doomguy, the Berserker Packin' man-and-a-half who takes on the hordes of Hell with his trusty shotgun (and chainsaw). That turns out to be enough, but still. Interestingly enough, the novels' interpretation of the Doomguy is a devout Catholic regardless.
  • Diagonal Speed Boost: Strafing and running forward simultaneously is faster than doing either independently.
  • Difficult, but Awesome: The BFG9000 is actually a tricky and unintuitive weapon to use to its full potential. It looks like it just shoots a big plasma ball that explodes into a large radius of splash damage upon contact with something, but how it actually works is that after the ball hits something, 40 invisible hitscan tracers shoot out from the player in the direction the ball was originally shot. As a result, if you're just running around firing off the BFG without keeping track of where you are when the BFG hits, you can have those tracers fire off in a completely unintended direction and have a lot or even all those tracers miss (for example, you shoot the BFG, you circle strafe around the enemies you shot at, and when the ball hits something, the tracers shoot off the side where there are no enemies). Then on top of this, the BFG has nearly a second of startup before the ball is even shot, adding to the difficulty in effectively using the BFG. If you can effectively manage the BFG's slow startup and can keep your aim steady towards the direction you shot and position close enough after firing, you can ensure those tracers hit their mark and deal out some really ridiculous damage (the ball alone deals between 100-800 damage to a single target, but the tracers can spread damage out and altogether can dish out over 3000 damage cumulatively - with some luck, you can potentially one-shot even a Spider Mastermind with that damage output). For an example of the difference this can make, if you're just circle-strafing around a Cyberdemon while shooting the BFG at it, it could take as much as 10 shots to take down if most of those tracers aren't hitting, but if you can keep your aim steady after firing, weave in between the Cyberdemon's rockets, and time the BFG to fire in point-blank range to ensure all tracers hit, you'll take down the Cyberdemon in just 2 BFG shots.
  • Digitized Sprites: Many monsters were made from clay and then converted to sprites.
  • Do Not Run with a Gun: The player is the only entity in the original games able to fire and move at the same time. Some mods change this.
  • Door Jam: Many traps in the first game and Doom II lock you up in a room with an army of monsters to kill, with the switch to open the door again being very well hidden, behind all those monsters, or non-existent (which forces you to search for a new path in order to find your way back). Notably is the 8th level of Doom II, Tricks and Traps, where you're thrown into a small room full of Baron of Hell and the strongest boss in the game, the Cyberdemon.
  • Do Well, But Not Perfect: The game shows off your item collection rate at the end of the level. If you don't particularly need these items due to playing well, your collection rating can be pretty miserable, especially on lower difficulties. This is mitigated by the fact that the only items that count towards this percentage are ones that you can pick up even if you don't need them, such as small health potions - larger health packs and ammo pickups don't count.
  • Downer Ending: The marine in the first Doom succeeds in escaping Phobos, climbing down from Deimos and escaping Hell itself, only to find that the demons have already invaded Earth, killing his poor little bunny and going on to do the same to most of humanity. The Ultimate Doom's fourth episode and the sequel, Doom II, have you saving what's left of humanity and it ends on a triumphant note, at least. There's even a miniature downer ending in the first episode, where you're transported into a darkened, inescapable room full of demons, and it's Lampshaded by the game-ending text. Thankfully, you survive to go on to the next episode.
  • Downloadable Content: The 2019 suite of Unity ports received an update that allows players to download curated mods for these games for free through Bethesda.net, such as both halves of Final Doom for both games, Sigil for Doom, and No Rest for the Living for Doom II with other mods added through content updates.
  • Drought Level of Doom:
    • "Hell Beneath", the first level of the new episode from The Ultimate Doom, is known as one of the hardest levels in the classic Dooms, due to the very little ammo and health that was on the map when playing UV difficulty. Even with the level's hidden Rocket Launcher, killing everything without having to use your fists is impossible unless you can bunch up the Barons at the end and spread enough splash damage across them with the few rockets you have. Plus since it's the start of the episode, players have to always Pistol start it. The Playstation/Saturn port would alleviate these issues by adding a couple Medikits from the lower difficulties and replacing all the Barons with Hell Knights that required a lot less ammo to kill, while the lack of episodes in those ports meant players didn't have to Pistol start the level either.
    • In the Jaguar, Playstation, and Saturn ports of Doom 1 they have a new map called "Hell Keep" to replace the PC's original Hell Keep, and it's infamous for having very little ammo, where on Pistol start you can't kill everything on UV difficulty without using your fists and/or exploiting infighting. The map also has little health with only three Stimpacks and two Medikits, the latter of which don't become available until near the end of the map, and unlike the aforementioned Hell Beneath, it doesn't even have the courtesy to give you any armor. Since Doom 1 is played as a single long episode in those ports instead of the multi-episode structure it originally had, players do not need to Pistol start it and so can bring their ammo and armor from the previous map to alleviate the issue, but those that choose to Pistol start it found surprising difficulty when these ports were known for being usually easier, especially since the original Hell Keep was such an easy map.
  • Dual Boss: The two Barons of Hell at the end of the first episode of the original game. They get a repeat in Doom³.
  • Dude, Where's My Reward?: After defeating the Bruiser Brothers at the end of the first episode, you run onto the exit portal and are teleported to a zone where you can't see anything but hear nasty monsters all around you and immediately start taking damage until you are about to die. Then the end screen comes up expressing your expected outrage for you: "Where's your fat reward and ticket home?" etc. Even the ending of the third and final episode of the full game is not entirely satisfactory, due to the scene which greets you after you "get home".
  • Dungeon Bypass: Many levels can be completed in seconds by exploiting glitches to create shortcuts. In source ports that allow jumping, you can end certain levels within seconds by leaping onto the otherwise inaccessible exit switch/linedef.
  • Early-Installment Weirdness:
    • The game is broken up into four shorter episodes. Later games would have the campaign be one long, uninterrupted string of levels instead.
    • The Super Shotgun isn't in this game, which feels jarring as it would later be treated as one of the Doomguy's Iconic Items, his go-to weapon for situations that don't quite warrant the BFG-9000. Some fans who haven't played the original Doom don't realize that this weapon isn't in this game — the Super Shotgun doesn't get introduced properly until Doom II.
    • Some of Doom's most iconic enemies, such as the Revenant and Archvile, are absent from the first game.
    • The game has two episodes on the moons of Phobos and Deimos, but this plot point was later dropped and later games would have Mars be the key planet rather than its moons. This is presumably due to colonizing Mars being much more realistic than its low-mass moons.
    • The original game was divided into three episodes, with a fourth being added in the Updated Re-release Ultimate Doom. The player cannot take weapons and powerups from one episode to the next, making each episode's gameplay self-contained. This system is a relic of the game's Shareware origins; the first chapter, Knee-Deep in the Dead, was available for free, and players had to mail-order the other two, also leaving them to have to deal with that existing framework when they added a fourth for the retail release. Notably, this only actually gets directly explained in the transition to the second episode, where the protagonist is ambushed at the end of the first episode, dies, then wakes up in Hell. Doom II: Hell on Earth dropped this system as part of the shift to becoming a retail game from the start, with distinct "episodes" being an afterthought at best, only really differentiated by text dumps between them and changes in the sky texture which didn't even work under normal conditions.
    • The first game, in turn, has the first episode showcase some major differences from the subsequent three, and by extension the following Doom games. Besides being distributed as shareware, it's the only episode whose last level doesn't end with a standard boss battle (standing in for a Dual Boss are two Barons of Hell, which are also the only ones in the episode); and defeating them isn't an Instant-Win Condition, as Doomguy still has to enter a portal where he is seemingly killed (though he is later revealed to be still alive). In terms of scenery, this episode is also the most grounded in reality, as none of the playable areas have yet become as twisted or corrupted as those of the second episode, and obviously the areas set in Hell don't appear until the third and fourth episodes. Lastly, the level design is the most rudimentary, which is attributed to the style and philosophy of John Romero (who designed all levels for this episode except two and didn't work on the other episodes' levels except two for the fourth).
    • The BFG is very different in this game and its derivatives. The green sphere doesn't shoot lasers at targets as it flies by, travels much faster and the blast effect is less intuitive. Later instalments like Doom³ and Quake made the blast more like a super rocket explosion, added the damaging radius around the sphere while it travels and made the sphere much slower. Ammo capacity also tends to be much more limited with Quake IV's Dark Matter Gun being a notable exception.
    • Early console ports, aside from missing maps and enemies, had maps with significant alterations or even some entirely different content. Most notably the PlayStation Doom port, which aside from combining Doom I and II together, and missing things such as some maps and the Archvile, featured a lot of radically different content. This includes featuring a completely different horror-based ambient soundtrack, entirely new sound effects, colored lighting, a new enemy in the form of the Nightmare Spectre, a significantly nerfed Revenant, and some new maps, including a new final map in both games. Later console ports from the sixth generation of consoles onward would be more 1-to-1 ports of the original games, with only some minor alterations to content (mainly censoring the red crosses on the medkits and the Nazi imagery in Doom II's Wolfenstein 3D maps).
  • Earn Your Happy Ending: After destroying Mars, venturing home to Earth to find that it's been taken over, saving the entirety of the human race, then venturing to hell and BLOWING HELL UP, Doomguy deserves this whole-heartedly.
  • Easier Than Easy: While it's not immediately obvious to the player, "Hey, not too rough" (the second difficulty) is the one internally labelled "sk_easy". "I'm too young to die" (internally "sk_baby") uses the exact same thing placements, but gives the player double ammo and halves their damage taken.
  • Elite Mooks: The Barons of Hell are degraded to this after the first two are defeated at the end of the first episode. They become regular enemies, but also tough ones.
  • Empty Room Until the Trap: This series gets off on this. You'll probably run into a seemingly empty room, maybe containing some goodies, until you fall into a trap where a horde of demons await to destroy you.
  • Endless Corridor: Although the original Doom actually helped break first-person gaming out of the "straight corridor" mode, there are still many locations in the first game and its sequels where the endless corridor effect is invoked.
  • The End... Or Is It?: The text-crawl endings to the non-PC editions of the original all suggest that demons may have made it to Earth. The PC version makes it abundantly clear with the cutscene following the text that, yep, they did. And the Doomguy's pet bunny Daisy was their first victim.
  • Epic Fail: What did the UAC want to do? Make teleporters. Result? Hell invades Earth.
  • Equipment-Based Progression: In the classic games, the player gets stronger as they find better and more powerful weapons, and finding your first ammo backpack permanently gives you double the ammo capacity.
  • Escaped from Hell: The Marine dies at the end of the first episode. Two episodes later, he finds a portal back to Earth as the ending text says he was "too tough for Hell to contain".
  • Exact Words: The game ends its third episode, "Inferno", with the Doomguy killing the Spider Mastermind and making his way out of Hell and back to Earth, with the ending text saying "It's good that no Hellspawn could have come through that door with you." Come the fourth episode of The Ultimate Doom, "Thy Flesh Consumed", and Doom II, you discover why that is: no Hellspawn followed you through the gate, because while you were busy fighting your way through Hell, the demonic legion had commenced their invasion of Earth! By the time you return to Earth, it's already Hell on Earth!
  • Excuse Plot: There was originally a long and complex plot with multiple protagonists. This was cut and the plot was reduced to: "You're the last Space Marine left on Mars. Shoot anything that moves." Obviously, this didn't detract from its success. There's also a "Go To Hell and Back" part, but that's not really important outside of giving you a chance for more demon-slaying.
  • "Everybody Dies" Ending: By the end of the first episode every single living character, no matter how minor, is confirmed dead. That's every single one of the scientists your crew was sent to check up on, every single one of your teammates no matter what station and the protagonist himself is killed in the episode finale to boot.
  • Everybody's Dead, Dave: This sets the stage for the first game when the hero is the only surviving member of a squad of marines sent to two demonically-overrun moons (go figure) and then Hell.
  • Evil Is Not a Toy: The UAC teleporting things around seems perfectly sound until you realize that to do this, they had to lay their lines through Hell. Hell's demons, none too pleased at their domain being reduced to an interstellar railway system for a bunch of worthless humans, decide to jump into the transport system and pay what's waiting at the other end a visit.
  • Evil Is Not Well-Lit: The Playstation and Saturn versions utilize colored lighting and shadows to give the levels a darker, gloomier feel.
  • Evil Tainted the Place: The first episode's levels are your standard sci-fi military installations and science facilities. The second episode's levels have more hellish influences creeping in, with demonic symbols appearing on walls and pillars, electronics suddenly giving way to wood and stone, rivers of blood and lava, gnarled vines growing on walls, and a blood-red sky. It turns out that Deimos has actually been transported to the skies above Hell.
  • Evil Versus Evil: You can set up scenarios like this quite easily, and some demon types, such as Cacodemons and Barons of Hell, actively despise each other.
  • Excuse Plot: Demons have invaded Phobos/Earth! Go kill them all in an over-the-top and gory fashion.
  • Expansion Pack:
    • The Ultimate Doom was a re-release of Doom featuring an additional episode.
    • The original Doom had an unofficial commercial expansion with no approval by ID called The Lost Episodes of Doom, which was originally sold with the book of the same name in 1995 and it came with a floppy disc containing a collection of three eight-level episodes. This expansion was originally made for the original Doom (v1.2-v1.9), not The Ultimate Doom, which caused some bugs and crashes to occur unless a patch was used for The Ultimate Doom.
    • Also among the unofficial commercial expansions included the infamous D!ZONE series released from 94 to 96, which were compilations of hundreds or thousands of fan-made WADs downloaded from the internet without any of WAD authors' permission. Given the lack of quality control and how primitive map-making was in that era, D!ZONE became known as a big pile of shovelware, with very few of the maps included being anything remotely decent. They were also infamous for exaggerating the number of maps they included, having a ton of duplicate WADs, having WADs that were just Doom 1 maps with Doom 2 enemies haphazardly thrown in, and their packaging having screenshots of simulated gameplay to give the impression of advanced graphics, while none of the WADs included remotely matched the screenshots.
  • Expressive Health Bar: The heads-up display includes a picture of the character's head. As the character takes damage, the head looks more and more hurt (bloodied and bruised). When the character has almost no health left, the head looks almost dead. If the character picks up the Invincibility Power-Up, the portrait will display Glowing Eyes of Doom. Receiving damage will cause the character to grit his teeth in pain, or (in certain versions of the game) make a shocked face.

    F-G 
  • Fake Difficulty:
    • Hitscan enemies can be placed in a way where your auto-aim fails to target them, while they're able to still fire on you. Hitscanners can also induce this in big open rooms, where avoiding getting damaged by them becomes a Luck-Based Mission as you cannot dodge their fire and you can only hope to get lucky with the RNG making their shots miss before you kill them. Fortunately for the player, hitscanners aren't often placed in such ways in Ultimate Doom and Doom II, though there are many poorly made WADs where this becomes a much greater and more frustrating problem.
    • The SNES port removed the ability to circle-strafe, making bigger enemies much harder to evade and defeat.
    • Teleporters can sometimes drop you right in the middle of a pack of enemies who will proceed to shave off a large chunk of your health before you can escape.
  • Fake Ultimate Mook:
    • The Cyberdemon is tall and imposing, with its first appearance in episode 2 showing that it mutilated four Barons of Hell in its lair. The actual enemy can be circlestrafed to easily dodge its rockets, and if dealt with perfectly, might end up dealing less damage to the player than a swarm of lowly hitscanner Mooks. Later games based on the engine (i.e. Plutonia Experiment, Doom 64) usually used level design perks (i.e. small rooms, tight corridor mazes) to prevent you from simply circle-strafing him to death.
    • The Spider Mastermind (Episode 3 endboss) is far easier to defeat than the Cyberdemon (Episode 2 endboss) not least because Episode 3 allows the player to use the original BFG. In addition, the Cyberdemon has more hitpoints (4000 vs. the Spider Mastermind's 3000). 3000 hit points, incidentally, is less than the maximum possible damage done on a close-range BFG shot, so unlike the Cyberdemon, the Spider Mastermind can be a One-Hit Kill for a lucky space marine.
  • Fan Remake: The PlayStation version of Doom has a total conversion on PC (requiring GZDoom), with some enhancements and side mods to recreate the feel of the original game. The project was abandoned due to lack of interest in supporting the project further and its dwindling compatibility with newer versions of GZDoom, but it has a modern spiritual successor in the form of DOOM CE which also covers Doom 64, incorporates other projects such as Beautiful Doom, the GEC Master Edition (DZDoom) project, and Doom 64 Retribution total conversion, includes various optional add-ons such as upscaled sprites, PBR materials, extended and arranged soundtracks, and other fan-crated mods, all while providing players a wide range of options to customize their experience with presets to make the games resemble their original counterparts, give them a modern overhaul, or a mix of the two styles.
  • Fireballs: Imps love throwing fireballs at you. Cacodemons spit them at you. Hell Knights and Barons of Hell hurl green fireballs that hurt a lot more.
  • First-Person Shooter: The Doom games were known as "Doom clones" for several years before games like GoldenEye and Half-Life did things Doom didn't and the name "first-person shooter" became common.
  • Fission Mailed:
    • You can still finish a level while dead (if your corpse crosses the exit line or if you've managed to kill the level's final boss), and you are alive again at the beginning of the next level (although with all of your things gone)
    • At the end of the first episode, you go into a teleporter and are "killed" by a group of monsters.note  Then you find yourself on the lost moon of Deimos, which happens to have been transported into the Hell dimension.
  • Five-Second Foreshadowing: Per the word of John Romero, the first dead body you come across in "At Doom's Gate" isn't just there to establish the mood; it's meant to be a clue that there are enemies just beyond the door nearest to the corpse.
  • Flaming Skulls: Lost Souls are floating engulfed in flames, and can be lethal when coming in large numbers.
  • Flashy Teleportation: Whenever a character or creature teleports, there is a burst of yellow/green energy at the origin and destination sites.
  • Follow the Money: The game uses a variation at one point: a secret area in E1M6 is pointed out by an arrow made up of small armor pickups pointing towards a wall.
  • Friendly Fireproof: Both the game and its sequels show a famous aversion. When two demons' attacks collide, they'll prioritize and attack each other instead of Doomguy. Causing monster infighting is actually encouraged on some levels, especially the one in Doom II with both a Spider Mastermind and Cyberdemon.
  • From Nobody to Nightmare: The protagonist starts out as some random marine contracted to protect a research facility in Phobos. One portal screwup and opening of Hell later, he goes on to singlehandedly save the base, prevent humanity's extinction, and completely wreck Hell itself.
  • From Zero to Hero: The backstory of the game is that the Marine was sent to Mars as a punishment posting, watching the researchers of the United Aerospace Corporation do science-y stuff. Once things get dicey with the UAC's dimensional teleporters, the Marines head to Phobos to check on things. The Marine gets left behind to guard the shuttlecraft with only a pistol while the rest of the squad takes all the fun toys and goes in for a look-see. After some gunfire and screaming, the radio goes silent. The lone Marine must now fight his way through hordes of hellspawn to get back home.
  • FTL Test Blunder: The backstory of Doom states that the Union Aerospace Corporation was experimenting with teleportation between the Martian moons Phobos and Deimos, but instead opened a portal to Hell and caused Mars to be invaded by The Legions of Hell.
  • Fun with Acronyms: In the 2019 Unity port version of the Back to Saturn X series, the mod's title was changed to simply BTSXnote  while using joke subtitles for their respective episodes with Better Texturing with Startan X for Episode 1 and "Big Towers", says Xaser for Episode 2.
  • Gainax Ending: The ending to the first episode is like this intentionally. After you beat the barons of hell, you enter a teleporter that takes you to a pitch-black room that's full of demons and has a damaging floor. Once your health gets under 11%, you seemingly die and the game cuts to an ending exposition crawl which lampshades how ridiculous this ending is after all you've been through. Most likely, this was meant as a sort of Sequel Hook variant as the shareware version only has the first episode to encourage people to buy the whole game to find out what happens to their character.
  • Game-Breaking Bug:
    • All walking monsters have infinitely tall collision hitboxes, and all melee attacks from monsters have infinitely tall damage hitboxes. While this is generally not a problem in stock Doom levels, this becomes one in custom levels with large amounts of monsters as it makes running off of edges much more difficult without being blocked or hurt by monsters that are right underneath you.
    • The PlayStation version has a TEXTURE CACHE OVERFLOW bug that crashes the game due to overloading the system's memory (especially on first-generation PlayStations) when a very large number of enemies are present.
    • Another PS1 bug that broke the game for anyone attempting to finish a level with 100% kills would sometimes occur if a monster was impacted by splash damage or was simply shot at when too close to a wall. The monster (this tended to happen most with the Lost Soul floating skull or any of the zombie soldiers) could be sent into the wall. The monster would still be visible and still in fact attempt to shoot or attack the player but would otherwise be unkillable (and unable to harm the player). Adding to the surreal nature of the bug, the monsters would then start moving off into the distance until they effectively vanished from view (but could still be seen using the show monsters map cheat). This glitch appears to be unique to the PS1 version of Doom proper and not the port of Final Doom.
    • The "all ghosts" bug, also known as "intercepts overflow", causes many aspects of collision to completely stop working if a hitscan weapon has to make more than 147 collision checks. This can be (relatively) easily performed in the Icon of Sin, by hiding in a corner and letting the Mook Maker boss spawn enemies for over two hours until there's a pile of corpses high enough to trigger the bug, but it can also randomly occur in any level with any shot due to a rounding error which, if it happens at the right/wrong time, can cause the game to overpopulate the intercept list with many copies of the same few intercepts. Thankfully for casual players, the rounding error is already extremely rare, and the timing requirement makes actually triggering the bug rarer still — and even if the stars do align and the bug is triggered after all, saving and reloading fixes it.
  • Game Mod: A large portion of Doom's appeal comes from its highly moddable nature, which Word of Godinvoked confirms is by design, building on the strong community response to map-making for Wolfenstein 3D, and desiring to make custom content creation more accessible (as well as to ease internal development)—game assets can be easily swapped with fan-made ones. The game engine's modular nature also means that Doom and Doom II are technically game mods themselves.
    • The source code for the game engine that powers Doom and Doom II, best known as the "Doom engine" (though officially known as "idTech 1" after id started making more game engines) was first released in 1997, then re-released under the open-source GNU GPL in 1999, then under the MIT License in 2014, which not only permits porting the game to just about anything with a CPU, controls, and a display but also gives an entirely new depth of game modding potential that allows for deep-level modification of the engine to completely reforge it. This has resulted in Doom having one of the most wildly varied modding communities, with some of the higher-quality mods making Doom look utterly unrecognizable, as well as the "It Runs Doom" meme, referencing the fact that Doom has been ported to a huge variety of electronic devices, including several that were not designed to run video games in the first place.
    • Nearly three decades after the initial release of Doom, new mods, map packs, and total conversions are still being made. TV Tropes has a partial list of game mods that run on the Doom engine here. Many more mods can be found at the /idgames archive or at the numerous message boards which are still fairly active. Another alternative would be to use a modern server browser, which comes with an auto-downloader.
    • Even Doom's console ports of the '90s and early 2000s have also seen their share of ROM hacks (especially when the source code of said console ports are released), many of which aim to restore missing or cut features compared to their PC counterparts, or in some cases, turn a rather poor conversion into one that's worth playing.
      • Doom 32X Resurrection is a project that takes the admirable but disappointing Sega 32X port and makes it more faithful with restored level geometry, better use of colors, adds the ability to save and load gameplay progress, more customization options, and a wealth of quality-of-life improvements. It also adds support for CD music playback in addition to replacing the infamous FM synth soundtrack with newer renditions that make better use of the Genesis's soundchip.
      • PlayStation Doom: Master Edition is a project based on the PlayStation ports of Doom that aims to backport all of the cut levels missing across Doom, Doom II, and Final Doom while porting No Rest for the Living, SIGIL, other custom levels created by John Romero, and Tom Mustaine's Doom2 Map14 Homage, all in the style and limitations of PlayStation Doom. Its Beta 4 release also adds new options and support for DualShock controllers.
      • The Game Boy Advance ports of Doom and Doom II have a pair of PC conversion ROM hacks that restore many features and visual elements from the PC version while improving music quality and sound effects.
  • Gang Up on the Human: Normally avoided, due to monster infighting - while monsters will never attack one another without provocation, they will retaliate when they hit each other, and generally continue until either you grab both of their attention again or one of them kills the other. Some complications go towards this trope though, as Lost Souls will only make a single attack on an enemy that hit it before turning their attention back to the player, or if the player is not in sight, going dormant (they don't retain targeting information after a counter-attack, successful or otherwise). A successful attack on an enemy still leaves that enemy angry at the Lost Soul.
  • Gatling Good: The Chaingun. It's been a series staple and can mow down most lower-tier enemies in seconds, while stunlocking a number of bigger monsters. The only time it becomes ineffective is against bosses, who have too much health and too little stun chance for the chaingun to be efficient against. Despite its threatening appearance, though, its fire rate and behavior are more akin to an assault rifle; in Strife (another Doom-engine game released a few years later), the weapon is even redrawn into a rifle, and behaves convincingly enough.
  • Glass Cannon:
    • Pinky Demons and Spectres on Nightmare difficulty move at twice the speed, as well as attack at twice the speed, giving them the ability to attack very quickly with their bite that does up to 40 damage per hit. However, they still have their low 150 HP, allowing them to be killed fairly quickly by anything but the Pistol.
    • The Marine himself is one; he moves far faster than every enemy in the game and can outrun their non-hitscan attacks, while his weaponry is far more powerful than what the demons possessnote . However, the Marine only has a base HP of 100 (even less than the aforementioned Pinky), and at max health and armor has the equivalent of 400 HP (which most higher demons exceed).
  • Glowing Eyes of Doom: The protagonist's eyes on the status bar become glowing and golden when an invulnerability power-up is taken (or God Mode is enabled). Combine with a Berserk Pack, and you too can have fun with puns!
  • Golden Super Mode: The Space Marine's eyes become golden upon picking up an Invulnerability, or when the God mode cheat is entered.
  • The Goomba: The zombie troopers, who have 20 HP (meaning even the fist can kill them in 2 hits) and wield nothing but a rifle with the same feeble stats as the player's noob pistol. But much worse accuracy. Because they're zombies. And they only remember they have a weapon at random intervals. Because they're zombies. And if by some miracle they manage to get their necrotised brain together long enough to score a hit, the damn bullet only takes a single digit of your hp. Intentionally getting killed by one is difficult. It might get bored and walk out of the room or injure an ally and fight to the death before it can finish you. Because they're zombies.
  • Gorn: One of the games of the 90s, alongside the likes of Mortal Kombat, that created the moral panic about violence in video games for a reason. The original alone had gory death animations for some of the enemies like Barons of Hell splitting in half to show their entrails and spinal cord, excess damage to weaker enemies (and the player!) turns them into red slop on the floor, and the environments were often decked out in corpses and gore the further you got into the games. In the modern era it's nothing special (some of the imagery can be on the unsettling side but that's the worst of it, with the violence itself being relatively mild) but in its age it was a wave of controversy.
  • Gray Is Useless: Doom has the numbers 2 through 7 on the status bar that represent the various weapons Doomguy can use. Doomguy always starts a level with the pistol, #2, but must collect better weapons in his travels. These corresponding numbers will be in dull grey until Doomguy obtains that weapon, although he can collect the ammunition for it beforehand.
  • Grimy Water: While green nukage and red-and-orange lava are always harmful, and the extremely blue water is almost always harmlessnote , whether or not brown slime and blood are damaging varies depending on the whim of the level designer. With custom WADs, no holds are barred: nukage and slime can be treated as algae-infested or plain muddy water, blue water can be electrified, or actually liquid nitrogen or reactor coolant, and blood can even be swam in; lava tends to be consistently damaging, however.
  • Guide Dang It!:
    • Some of the secret areas can reach this level. The Containment Area in Episode 2, for example, not only has a secret room within a secret room, but there's a secret passage within that secret room leading to another part of the stage, and there's another secret room within that secret passage. Those who are used to more linear, modern FPS games will also sometimes find difficulty in navigating most Doom maps, as they tend to include repeatedly moving through areas to acquire keycards and open locked doors.
    • The difference between basic armor (green) and mega armor (blue) isn't just the amount of armor points they give you (100 for green and 200 for blue), the mega armor also reduces damage taken by 50%, while the basic armor has a 33% reduction. However, there is no in-game indicator that the mega armor does anything more than just have double the armor points, and the game lets you pick up a green armor if you have less than 100 armor points, when it's usually beneficial to use up most of your superior mega armor first. Players as a result are often unaware that the armors has any different functioning until they find out from an outside source.
    • How the armor bonuses work in relation to the two armors can also be confusing. When picked up, an armor bonus will give you 1 armor point (or 2 in some of the early console ports and Doom 64), up to a total of 200. If you have no armor or green armor on when you pick them up, the armor will reduce damage by 33%. However if you do have mega armor on, the armor bonuses will add to its durability and thus keep its 50% protection, incentivizing further to try keeping your mega armor on as long as possible before replacing it with green armor.
    • There's then the Megasphere, which gives you 200 health and 200 armor. Again there's no indication in-game that its armor provides any different amount of protection, but the armor it gives you is effectively mega armor and thus has 50% protection.
    • The way the berserk powerup works is this: it's basically a black medkit that heals you to 100 health (unless your health is already higher) as well as increases the damage of your punches by tenfold, turning them from a joke to an actually viable melee attack. The confusion comes from the duration: most players believe it only lasts until the red tint it gives your vision fades (about 20 seconds), but it actually lasts until you leave the level or die. The reason for this is likely because the designers realized that having your vision be tinted red for the rest of the level would be really annoying, but it's still pretty confusing and counterintuitive, especially since the manual itself claims the effect is time-based rather than until the level ends. Additionally, any subsequent berserk packs you pick up on a map will still heal you up to 100 and temporarily tint the screen red but will not further increase the power of your punches.
    • The way the BFG works takes some experimenting to figure out or just looking it up, as the BFG ball doesn't explode into a big radius of Splash Damage like rockets do as many players initially assume. The way it works is when the BFG ball hits something and explodes, 40 invisible hitscan tracers fire from the player in a 45-degree radius towards the direction the player was facing when the BFG initially fired. At point-blank range, a Cyberdemon can be killed in just two BFG shots as all the tracers together can deal out over 3000 damage, but farther away, some or most of the tracers will miss or hit other monsters, or even all the tracers can miss if the player ran into a position that made the tracers fire off in the wrong direction, making it take much more BFG shots to take the Cyberdemon down.
  • Guilt-Based Gaming: When the player attempts to exit, a humorous quit message is shown, mockingly trying to convince the player to stay and play some more.

    H-N 
  • Hailfire Peaks: Starting from the second episode, many levels are built to look like techno-bases, but slowly turn into hellish architecture by the presence of the demons.
  • Hall of Mirrors: Doom has what is called the "Hall of Mirrors effect" which happens when someone uses the noclip cheat code to walk into the walls of a level. It can also happen when a texture for a wall or object is not properly referenced. It looks like part of the screen is shimmering, and everything is leaving behind a trace because the screen buffer is not being cleaned between frames. The Unreal engine also has this effect when the player somehow sees what's outside the level, either by noclipping outside or looking at a piece of a surface in the level geometry that has no texture. It can also happen if more than three warp zones are placed in a way that the player can see through all of them at once, like a Matrix-style endlessly looping tunnel: the first three zone portal surfaces properly stay invisible but the fourth and subsequent ones become visible and cause this effect, with mappers having to use fog to hide it. It greatly reduces rendering speed and can even cause the game to crash.
  • Hand Wave: The manual for the Atari Jaguar version puts the blame for the game's less-than-stellar performance during multiplayer on the fact that the game takes place in Hell... which is only true for the third episode.
  • Hard Levels, Easy Bosses: This and the other games on its engine have fairly unimpressive boss battles, with the Barons of Hell, Cyberdemon, Spider Mastermind, and (in the sequel) Icon of Sin all being relatively easy fights. This is especially pronounced on higher difficulties, which up the number of enemies substantially, meaning chewing your way through an entire army is now a much bigger feat. A lot of this is because common enemies make much more judicious use of Hitscan. The Spider Mastermind is the only aforementioned boss to use hitscan, but it also has lower health than you'd think and is easy to stunlock. Quite tellingly, a lot of fanmade hacks convert the Barons and the Cyberdemon into Elite Mooks and still end up fairly beatable (less so the Spider Mastermind, due to it being much harder to work with).
  • Hard Mode Filler: E3M9 "Warrens", the Secret Level in Episode 3, starts out as completely identical to the episode's first level. Until you reach the "end" and hit the "level complete" teleporter when the walls around you suddenly come down and you find yourself in a giant room with a Cyberdemon. Then you backtrack across the level and try to find the exit elsewhere, only to find more new enemies due to many areas having been opened from the moment you found the Cyberdemon; the level keeps going until much later when you find the real exit not too far from the starting point.
  • Hard Mode Mooks: Things that can appear on a map, including monsters, have flags that determine which difficulties they appear on, with one for "I'm Too Young To Die" and "Hey, Not Too Rough", one for "Hurt Me Plenty', and one for "Ultra-Violence" and "Nightmare". Going up in difficulty typically includes greater concentrations of enemies (E1M1: Hangar only has four zombies and two imps up to Hurt Me Plenty, then doubles both of those numbers and adds 16 shotgun zombies on Ultra-Violence), introducing stronger enemies sooner (the cacodemon is introduced in E2M3: Refinery on HNTR or below, and in E2M1: Deimos Anomaly on HMP or above), and/or even replacing lower-tier enemies with stronger ones (E2M1 has a Lost Soul on HNTR and below that's replaced with one of the cacodemons on HMP and up). The PlayStation version expands on this by allowing several Doom II-specific enemies to appear in Doom 1 levels on higher difficulties, such as E1M1 including a Chaingunner and Pain Elemental on Ultra-Violence.
  • Hard Mode Perks:
    • "Nightmare!", for all it does to make the game more of a, well, nightmare, still gives Doomguy double the ammo for every ammo pickup.
    • On Ultra-Violence and Nightmare!, Hangar has Shotgunners and, in the PS1 version, a Chaingunner, allowing Doomguy to get their respective weapons earlier.
  • Harder Than Hard: The aptly named "Nightmare!" difficulty, the only setting where monsters you've killed will respawn several seconds after they die. The monsters also shoot more rapidly than on all the other difficulty levels. And cheat codes are disabled. The only good thing about it is that ammo pickups contain double the normal levels of ammo like on the easiest difficulty... and you will need it all. "Nightmare!" wasn't even included in the earliest releases of the game, only added with v1.2 after more hardcore players complained that Ultra-Violence wasn't as difficult as they'd hoped. It's very hard in single-player mode, but it's fine for co-op multiplayer games, which lets the players respawn, too.
  • Have a Nice Death: ZDoom-based source ports by default display various obituary messages in the heads-up display based on which monster or hazard killed the player, e.g., "Doomguy was splattered by a Cyberdemon." Some of the monsters have two obituary messages based on whether the monster that killed the player used a melee or ranged attack, e.g., "Doomguy was slashed by an Imp." for the claw-slash vs. "Doomguy was burned by an Imp." for the fireball.
  • Hazmat Suit: You can find them on certain levels. They allow you to walk through toxic waste without any harm for a limited time. They also protect you from other hazards like lava and boiling blood.
  • Heart Container: Health and armor bonuses respectively can raise your health and armor past 100, though you cap at 200 and regular medkits will never raise you above the default 100. Soulspheres gives you an extra 100 health, Megaarmors gives you 200 armor points instantly.
  • Health/Damage Asymmetry: The demons have very high health but weak attacks, while Doomguy is much flimsier but able to deal ridiculous amounts of damage. The only case where a demon has offensive power on par with the player is the Cyberdemon — the big guy's rocket launcher is exactly the same as yours. Now let it sink in that the rocket launcher, while definitely powerful, is not your most devastating weapon.
  • Heal Thyself: Doom implies that the healing pickups have small doses of Super Serum (though that puts it in the territory of Instant Sedation). Berserk Packs drop the "implied" part, instantly bringing you up to 100% health from any amount below — even right at the brink of death with a single hitpoint — and make you strong enough to tear zombies and imps apart with one punch for the rest of the level. Soulspheres and Megaspheres (which respectively add 100 health, up to 200, and give you the full 200 health and armor) are more justified since they're black magic.
  • Healthy Green, Harmful Red: Most versions, up to the Collector's Edition, have hazardous floors in some levels, which are radioactive sludge or molten ooze. There's usually a hazmat suit nearby if the sludge area is large enough. When the suit is used, the player's view takes on a greenish tint for as long as the suit lasts and renders the player immune to the floor's normal damage. When there's no suit available, or its duration expires, the floor resumes its damage, which turns the player's view into a reddish tint while his health percentage declines.
  • Hell: The various games in the series involve teleportation experiments in a future space setting that have accidentally opened portals to Hell. Something of a Hyperspace Is a Scary Place plot, except the games make it clear that what the scientists call hyperspace actually is Hell, which is mostly portrayed with seas of lava, brimstone mountains, and a burning red sky.
  • Hell on Earth: How the original game ends. After literally going through Hell and returning to Earth, you find that Hell has followed you home.
  • Hellgate: Not in the traditional sense as the teleportation system that the demons of Hell hijacked was merely a UAC conduit that used Hell as a pass-through wormhole in order to move matter across great distances in trivial amounts of time. The demons simply interjected themselves in the conduit, like a living phone tap, and invaded at both endpoints.
  • Helpful Mook: Almost any enemy can be helpful since enemies can damage each other, causing them to infight. This is an important tactic for higher difficulty levels.
  • Heroic Lineage: Doomguy is the son of Billy Blaze, the protagonist of Commander Keen. He's also the grand-grandson of William "BJ" Blazkowicz, the protagonist of Wolfenstein 3-D.
  • Heroic Mime: Doomguy (with the exception of the Comic) doesn't seem to have a whole lot to say. This may be because there is nobody to talk to. But he can express himself with the great communicator.
  • Hero-Tracking Failure: Enemies have no idea how to lead their shots, meaning they're helpless to a player circle-strafing around them. The FPS convention of using the mouse to aim began as a pro-skills tactic for Doom — the default control scheme exclusively used the keyboard and made moving and aiming simultaneously almost impossible.
  • He Who Must Not Be Seen: The original game made this famous - the only reason anybody knows what he looks like is the face in the status bar.
  • Highly-Conspicuous Uniform: The Marines wear sensible fatigues, but their body armor comes in Day-Glo Lime Green and Peacock Blue.
  • Hitbox Dissonance: The game has a litany of these, and most are kept in vanilla-accurate source ports.
    • Everything is essentially treated as having infinite height, allowing monsters to body-block and melee players even if they are hundreds of meters apart vertically.
    • The Spider Mastermind seems to take up space at least four feet farther on each side than it appears. This often leads to it getting hung up on walls and other monsters when used in custom levels.
    • The plasma rifle has the "projectile's hitbox is too large" variety, while the Mancubus's fireball has the inverse problem of a too-small hitbox, to the point where they can clip straight through walls.
    • Hitscan attacks (bullets, BFG tracers and melee) can completely fail to hit their target depending on where the shooter and the victim are standing in open space, even at point-blank range. This is due to the blockmap bug: hitscan collision is registered when the hitscan attack's trajectory line touches the cross-sections of the target's bounding box, but if the hitscan line and the cross-sections intersect in a blockmap where the centre of the bounding box is not, the collision check fails. This also makes melee-ing large enemies extraordinarily difficult. ZDoom and derivative source ports fix this issue by changing the collision check to consider the edges of the bounding box, exactly like projectiles do in vanilla.
    • Projectiles that impact with the "ceiling" of sectors that have an open sky immediately despawn. This is rarely triggered without using freelook, however, and tends to be of little consequence when autoaim sends a projectile into the skybox, as that means it missed the monster it aimed at anyway.
    • Due to the pseudo-3D gameplay and the way in which maps are created, switches can be triggered even if you're not physically on the same level as the actual graphic for that switch. Hac X MAP16 in particular can be completed in one second because the exit switch is in the same area the player starts the level in, just hidden underground until the player finds and uses four other switches throughout — just turn around and use the empty air behind you.
  • Hitscan: All bullet-based weapons and the invisible part of the BFG's fire cycle in the first two games. In some cases (particularly Nightmare difficulty) this can make zombiemen even worse than their tougher imp counterparts. At least with imps you get a chance to dodge the projectiles that get shot at you.
  • Hollywood Darkness: The original Doom is one of the first games to make use of varying light levels between sectors and a dark fog effect to scare and disorient the player. I.E.: pick up a critical key, the lights go out, monsters appear. The only light sources in these situations were the very rare light amplification visors and the Muzzle Flashlight, though modern source ports can support dynamic lights or even limited raytracing.
  • Hopeless Boss Fight: Episode 1 of the original game ends this way. Right after defeating the Dual Boss of Barons of Hell in the last level, you get teleported to a dark room full of monsters, with a floor that not only drains your health but also turns off the god-mode cheat if in use, and you can't move; apart from shooting the monsters, all you can do is wait for your health to drop to below 11%, which ends the game. This can be overcome with cheating somewhat if you use IDBEHOLDV (granting you an invulnerability sphere), which isn't affected by the god-mode disabler. However, even if you kill the monsters, you're stuck there unless you noclip and there's no other way to beat the level.
  • Hybrid Monster: Cyberdemon has a rocket launcher for an arm, one robotic leg each, and wires for a midriff.
  • Hyperspace Arsenal: Where is the Doomguy keeping all of those weapons, as well as their ammo, is a mystery. At the start of the game, the player can hold 50 full-sized rockets, in addition to other ammunition and weapons. When you later find a backpack, you double your ammo-carrying capacity. A hundred explosive warheads are rather impossible to fit inside a military-grade backpack, and that is not accounting for your twenty kilos of bullets and five full boxes of buckshot. The novelization made an attempt to justify this by explaining that these were cutting-edge space-age mini rockets about the size and shape of a "D" battery.
  • Hyperspace Is a Scary Place: Hell was stumbled upon through teleportation experiments.
  • Iconic Starter Equipment: Doomguy/Doom Slayer is always seen using one of three weapons: the starting Pistol, the (sometimes starting) Shotgun or the Super Shotgun, the (usually) first weapon he stumbles upon during the first levels of his games.
  • Idiosyncratic Difficulty Levels: The difficulties are split into three categories; "easy" difficulties, a single "medium" difficulty, and "hard" ones, which add more and tougher enemies as you go up. The manual also has explanations for them:
    • I'm Too Young to Die: "An easy romp through the playground. Not many monsters here. This is good when you're learning the controls." The player gets doubled ammo from pickups and takes half the damage from enemies.note 
    • Hey, Not Too Rough: "This is good when you know how it works, but you still panic too much. Panic is a bad thing when you're surrounded by evil." Same amount of monsters as ITYTD, but your ammo pickup rate and damage taken are normalized.
    • Hurt Me Plenty: "The demons are out in force, and they'll take great pleasure in hurting you as much as you let them." The middle difficulty, adding more monster spawns to the levels and/or replacing some spawns with tougher enemies.
    • Ultra-Violence: "So you think you're tough? Prove it!" Even more enemy spawns are added.
    • The v1.2 patch added NIGHTMARE!: "This is for those times when killing a guy once just isn't enough. If you're lucky, you'll wake up..." Same enemy spawns as Ultra-Violence, but now they move and attack faster, respawn shortly after dying, and cheats (except for level-warping and giving yourself the effects of a computer area map) are disabled. The game even gives a second prompt when you try to select it asking if you're sure and admitting that "this skill level isn't even remotely fair". You at least get doubled ammo like on ITYTD, because you're gonna need it.
    • The 2019 Unity ports added Ultra-Violence+: same as regular Ultra-Violence, but with the turbo enemies from Nightmare as well as things that normally only spawn in co-op modes appearing.
  • Idiosyncratic Episode Naming: The level names of fourth episode in The Ultimate Doom, as well as the name of the episode itself, are phrases taken from the Bible: Thy Flesh Consumed, Hell Beneath, Perfect Hatred, Sever the Wicked, Unruly Evil, Against Thee Wickedly, They Will Repent, ...And Hell Followed, and Unto the Cruel. The exception is the secret level, whose name is simply Fear.
  • Idiosyncratic Wipes: The classic screen melt effect in every transition from the original. Some source ports add some extra wipes.
  • Immune to Flinching: Each monster has what is called a 'pain chance', which is the probability that they will go into a pain state after being hit with an attack, which temporarily prevents them from retaliating. No monsters have a 0% pain chance but, in general, the stronger the monster, the lower the chance will be.
  • Imperial Stormtrooper Marksmanship Academy: Enforced with the Partial Invisibility power-up. Enemies can still see you (at least once you give yourself away by shooting), but since it implies that they can only tell the general area you're in, it drastically reduces enemy accuracy and causes them to fire wildly in your vicinity.
  • Improvised Weapon: The trusty chainsaw serves as an upgrade to your melee attack.
  • Instant-Win Condition: Once you trigger the exit condition of a map, whether it be activating an exit switch, triggering an exit linedef, or killing a boss monster whose death ends the level, you win and advance to the next map (or ending if it was the last map) no matter what, even if you're dead while triggering the exit. In fact, your corpse can still trigger linedefs, so you can die and then have your corpse slide over the exit linedef to clear the map.
  • Instructive Level Design: The very first room you start in E1M1 is meant to be a safe zone with no enemies or anything that will actively attack the player, and allows players to get used to the controls, with even something to shoot at (explosive barrels, which players will quickly learn their use). Allegedly E1M1 was the last level to be designed, as the developers wanted to invoke this trope.
  • Insurmountable Waist-Height Fence: Central to much of the level design of the first two games, which did not feature any kind of jumping. Later source ports added jumping, allowing players to skip huge swaths of the classic levels by simply hopping over these obstacles.
  • Interquel: The Ultimate Doom, which was published after Doom II, contains a fourth episode for the original Doom, which occurs between the end of the third chapter of Doom and the beginning of Doom II.
  • In the End, You Are on Your Own: In the first game, the Doomguy is the Sole Survivor of the demonic invasion from Hell on the Martian moon bases. All the other humans have either been killed or zombified.
  • In the Style of: Bobby Prince's music for the game is based on heavy metal — John Romero lent Prince a set of metal CDs for reference, and thus the soundtrack is filled with familiar songs.
  • Invincibility Power-Up: Some levels have a green sphere that grants you temporary invincibility. While it's active, your character portrait has glowing eyes and black-and-white vision, but only for attacks dealing up to 1,000 damage in one blow. If an enemy or another player teleports or spawns onto your exact position, it does 10,000 damage, which is way more than enough to kill anyone.
  • Invisibility Cloak: Some levels have a Partial Invisibility power-up; this doesn't make it impossible to see the character, just extremely difficult, and those with ranged attacks have a random deviation added to their shots (e.g., fireballs veering off something like 45 degrees from where you actually are at the time; the powerup is rather infamous among the player base since in practice, as you'll typically be strafing to avoid enemy fire, it actually makes them better at hitting you because now they can "accidentally" compensate for your movement). The Spectre also has this effect, albeit permanently turned on.
  • Invisible Monsters: Specters are almost-invisible versions of the pink Demons, and are practically invisible in dark areas.
  • Jack of All Stats: The shotgun fills this role, in an early aversion of Short-Range Shotgun. It doesn't excel at any given category, but there are very few situations it isn't at least useful, with short-to-medium range, reasonable ammo consumption, good damage, and its status as a hitscan weapon ensuring that few things can go wrong when you fire it.
  • Jump Physics: You can't jump, but you can fall fifty feet without getting hurt.
  • Just Think of the Potential!: Nearly anything the United Aerospace Corporation tinkers with. As noted in the backstory, they had good intentions, but the lack of grasp regarding the nature of Mars and its moons left them unprepared against the demonic forces that are present there.
  • Kaizo Trap:
    • Opening an exit room door often reveals one last enemy waiting to take a bite out of any player who thinks they're in the clear.
    • The sixth level of Episode 2, Halls of the Damned, has a fake exit switch that instead dumps you into a room with a Cacodemon and a ton of Zombiemen.
    • Episode 3's secret level starts as an exact duplicate of the first map in the episode, until you step on the exit tile and the walls drop to reveal the boss of the previous episode. You have to go back the way you came (with every room now filled with more enemies) looking for a key for the actual exit in the first room.
  • Kick the Dog: The demons kill a bunny and stick the poor thing's head on a spike as they invade Earth at the end of the original game. The Ultimate Doom reveals that the bunny was Doomguy's pet, making this even more personal.
  • Kill Enemies to Open:
    • "Phobos Anomaly" (E1M8) requires you to kill both of the Barons of Hell to lower the star-shaped walls in their arena, which reveals a large courtyard with the teleporter to the exit.
    • "Against Thee Wickedly" (E4M6) has a particularly nasty example where a Cyberdemon shows up near the barred-off exit. The only way to raise said bars is to actually kill the Cyberdemon, and the space you have to fight him is generally very small, so good luck.
  • Kill the Lights: Picking up the blue key in the third map of the first game extinguishes all the lights in the room and opens a Monster Closet full of imps. The Imps are as accurate with their fireballs as ever; the player character, not so much.
  • Knockback: Doom was one of the first FPS games to implement basic physics for knockback, generally tied in with how damaging the attack is. Most notable is its use in accessing the third episode's secret level. A good shotgun blast or rocket hit was also the only way for non-flying enemies to fall off high ledges. The physics behind are also surprisedly sophisticated for such an early example, mainly that enemies had varying mass that also affected how readily they could be knocked back, and having a value that can give a weapon/projectile higher or lower knockback, relative to its damage (which generally can only be tweaked using source ports or mods). For instance, the chainsaw delivers no knockback to ensure it has the intended effect of ripping into targets rather than pushing them away.
  • Kubrick Stare: As Doomguy takes more damage, his head dips lower and lower, producing this effect.
  • Ladder Physics: The game lacks actual ladder behavior. A common trick used by modders to get around this is to create a set of stairs with extremely narrow steps, forming a nearly vertical ramp that can be ascended like a ladder (the issues of getting on them from the top without splattering yourself are avoided by the game completely lacking falling damage). Later source ports allow map creators to designate the area in front of a ladder as being underwater, allowing players to "swim" up the ladder, though with the caveat that, since drowning in underwater sectors is determined on a per-map basis rather than per-sector, using this trick together with actual underwater segments results in either ladder that you can somehow drown on or the Doomguy having Super Not-Drowning Skills.
  • Lantern Jaw of Justice: Doomguy's sprite portrait reveals his huge, square chin (apparently a family trait, as John Romero and Tom Hall indicate he's a direct descendant of Wolfenstein's B.J. Blazkowicz).
  • Last Note Nightmare: At the end of the game, you're teleported back to Earth after fighting through the legions of Satan and the fires of Hell itself, treated to a scenery shot of a frolicking meadow before noticing that the demons got here first. The music reflects this.
  • Lethal Joke Weapon: If you pick up a Berserk Pack, then your fists become this. After picking up said power-up, your punch does tenfold damage for the rest of the map, up to 200 damage, enough to splatter zombies and Imps, one-shot Pinkies, and kill bigger demons in a few punches. The problem is you still have to get in melee range and your punch has short reach, making your fists still seem like a joke, but with Doom Guy's incredible mobility, it is possible to safely weave in, throw a punch as you weave in, and then weave out before the enemy can hit you. Players who learn how to effectively do this will find genuine utility from Berserk, letting them kill enemies faster than they can with the Shotgun and Chaingun, and save ammo, especially against bullet sponges like Barons. It's also surprisingly useful against Revenants, who will only try to punch you if you're close to them, and since your punch consists of a single hit, it will have a low chance to trigger their pain state, unlike the Shotguns that are nigh guaranteed to (which you want to avoid since they'll always immediately retaliate out of their pain state with their missile attack).
  • Lethal Lava Land: "Mt. Erebus" is set on islands in a lake of lava, presumably the caldera of the titular mountain.
  • Level Goal: Flipping a switch located behind a black door marked with a golden square emblem ends the current level.
  • Level in Reverse: The secret level for Episode 3 is, at first glance, a room-for-room repeat of the first level of the episode, but with the original final room expanding into a boss arena when you hit the switch—the rest of the level has you going backwards through it, with all the rooms similarly expanded and with new enemies in them.
  • Level-Map Display: You can always look at a map of what you've explored so far. If you find a computer map, you can see the entire level. The exception is E1M8: Here the computer map is given to you right from the beginning. The level is named "Phobos Anomaly", but the map does not show the anomaly itself...
  • Lightning Bruiser: Cyberdemons are one of the fastest enemies in the game both movement and attack/projectile speed-wise while having significantly more HP than every other enemy in the game with a massive 4000 alongside a low pain chance and complete immunity to splash damage, and their rockets are just as strong as a player's, meaning they can kill you in one-two direct hits and easily lay waste to every other enemy in the game except the Spiderdemon in close quarters.
  • Literary Allusion Title:
    • The name Doom was chosen as a Shout-Out to Tom Cruise's pool cue in The Color of Money. (No, really.)
    • Episode 3 ("Inferno!") and its levels are named after Part 1 of Dante's The Divine Comedy.
    • As noted above, Episode 4 ("Thy Flesh Consumed") and its levels are named after Biblical passages.
  • Lock and Key Puzzle: The closest thing there is to a puzzle in the classic games. There are three different keys (red, blue, and yellow, all three in "keycard" and "skull key" variants, but only one variant appearing per level), each of which opens matching-colour doors within the same level. Which keys appear (if any) depends on the level, and the format depend. Later on, fans cooked up source ports that allow the game to distinguish between key formats as well, so in custom WADs, a man-made electronic keycard doesn't open.
  • Logic Bomb: In early versions of the classic games, monsters can fight each other if they hit each other. But if they somehow hit themselves (typically via barrels, as detailed in this article), they will tear themselves apart.
  • Long Song, Short Scene:
    • The song "At Doom's Gate" is only played for the first map of the first episode, and it's a very short map.
    • Zig-zagged with "Intermission from Doom", the intermission music: it's just over 3 minutes long, but the intermission screen itself gives little incentive to stay on it for more than a few seconds. On the other hand, it's also played as the background music for E2M3: Refinery, which is long enough that it's easily possible to hear the song in full without having to stand around doing nothing at any point.
  • Lost Pet Grievance: At one point before the events of the game, Doomguy had a pet bunny named Daisy. The demons killed her during their rampage across Earth, sticking the poor thing's head on a spike in the final image of the original game. All this did was piss him off even worse than he already was at what the bastards were doing to his planet, and to say it didn't end well for the demons is something of an understatement.
  • Ludicrous Gibs: Dealing enough damage will make certain monsters burst into red splatters.
    • If lesser enemies (or players in Deathmatches) are hit with an attack that reduces their health to their starting health times negative one (e.g. negative 30 for a Shotgun Zombie, who starts with 30 health), they will be gibbed. This is a reasonable result when they're hit by rockets, especially since ballistic weapons (e.g. the shotgun) are coded to not be capable of gibbing enemies even when they do that much damage, but picking up a special "Berserk" power-up enabled the player to gib enemies with his bare hands.
    • Sometimes you can melee-gib enemies even without the Berserker.
    • The Cyberdemon requires a lot of damage to be killed, 45 rocket hits, 55 shotgun blasts, or 400 handgun shots. No matter how much damage he's taken, he never shows so much as a dent until he is killed, but his only death animation is him exploding and leaving behind a pair of bloodied hooves. You can shoot him in the face with a shotgun 54 times, and he still has no visible damage, but he would vaporize when next hit by one bullet.
  • Make Way for the New Villains: For the first two episodes of Doom, the Barons of Hell are easily the biggest, baddest and toughest demons you go up against, and starting with their introduction at the end of episode 1, you fear them and know they're a force to be reckoned with. Then you reach "Tower of Babel", the final map of episode 2, and find yourself in a room with four Barons... all dead, horribly mutilated and strung up on the walls. If these were the biggest, scariest enemies in the game, what in the world did this to them? Then you meet the Cyberdemon. While Barons do still show up later in the games, this moment makes it abundantly clear that they're hardly the nastiest things you'll have to face.
  • Malevolent Architecture: The original batch of games says that the influence of hell has changed the layouts of many of the proper Earth levels. Once you enter Hell itself, all bets are off. Keys in Hell itself are an explanation of Benevolent Architecture.
  • Marathon Level: Going by the "par time" at the end of the levels, E2M4 and M6 are six and four minutes respectively, while it usually never goes to three minutes. Most maps in Episode 3: Inferno are really long and convoluted as well.
  • Mascot Mook: The Cacodemon, thanks to its somewhat goofy round design and relative ineffectiveness as an attacker, is widely considered to be cute by the community, enough for Hissy to become the mascot of both the Doomworld forums and the wiki.
  • Maybe Magic, Maybe Mundane: The original two games are somewhat ambiguous as to whether the demons are really demons from hell or just aliens from another dimension who happen to look like demons from Judeo/Christian mythology (indeed, they are even referred to as "aliens" in some of the text crawls and the book series explicitly says they are really aliens). Doom 3 and the 2016 Doom outright state they are demons from hell.
  • Meaningful Name: The third episode of Doom (Inferno!) draws its name from The Divine Comedy. The fourth episode (Thy Flesh Consumed), and its levels except the secret level (Fear), draw their names from Bible quotations.
  • MegaCorp: The Union Aerospace Corporation (UAC), a large government contracting firm that operates on the moons of Mars. While initially, they have no harmful intentions, they have been screwing around by using Hell as a pseudo-wormhole in order to teleport things between their Phobos and Deimos bases. This, predictably, Goes Horribly Wrong and demons begin pouring out of the teleporters at Phobos while Deimos just disappears entirely. Later games give them a more insidious slant (particularly the 2016 game, which sees them using Hell as an energy source and Samuel Hayden trying to downplay the UAC's complete disregard for potential consequences, while another faction of the corp is an out-and-out demon cult led by the Big Bad).
  • Medium Blending: Most of the enemy sprites, as well as Doomguy's, are made with Stop Motion, but some like the Imp and Cacodemon are hand-drawn, and the Former Humans are Head Swaps of Doomguy whose heads were hand-drawn rather than clay models. Nonetheless, they all blend seemlessly.
  • Minus World:
    • Some of the largest levels have enormous rooms filled with hundreds of monsters to teleport around. Occasionally the architecture that moves them into the teleporters glitches out, leaving a couple of monsters unteleported, simply sitting there; in those instances, noclipping inside the rooms is the only way to get 100% kills.
    • Noclipping out of the map will cause the Hall of Mirrors effect where everything repeats.
  • Missing Secret:
    • In some versions, the Percent kills/secrets/items count at the end of the level will always display 0% if the level doesn't have anything of that category. This gives the impression that the secrets are there, but you just didn't find any of them.
    • Some old level-design books actually suggest making a "secret area" trigger that can't be reached, so that players will continue to search for it.
    • There are also some official levels where it is impossible to get 100% secrets. Such is the case of Ultimate Doom maps E4M3 and E4M7 due to bad map design; the former has secret sectors with torches on top of them, the latter an invulnerability sphere that you can't reach and a door that's too thin for the secret to register. These can be triggered by noclipping, however.
    • The console ports of the early Doom games, which use somewhat redesigned levels, often didn't bother redoing the secret flags, making tons and tons of non-existent secrets still count as "not found" on the secret counter.
    • There are also several instances where getting 100% items isn't possible due to said items not being flagged as multiplayer only in deathmatch areas. Map 6 of 'Requiem' for example has two berserker packs unobtainable in single-player mode because of this.
    • The many, many, many console versions of DOOM sometimes do this with enemies. One level of the 3DO Interactive Multiplayer port has a hidden Imp you can only kill by shooting into a blank wall.
  • Modular Difficulty: The "-fast" switch makes all enemies move faster and shoot quicker than normal; this is the default only on the Nightmare setting on the main menu. Hellspawn fling fireballs aplenty right after their "alert" noise, pink demons (and spectres) charge at the player at a dead run, and hitscan enemies soon become Bullet Hell generators.
  • Monster Closet: The Trope Codifier, along with Teleporting Keycard Squad. Often times rooms would be just a pedestal with an item on them, but taking the item opens up all the walls to reveal nasties. If you see a key or very good item, expect the baddies to pop out as soon as you get it.
  • Mook Maker: Doom II adds the Pain Elemental which shoots out Lost Souls. The final boss also creates random enemies as well.
  • Moral Guardians: Along with Grand Theft Auto and Carmageddon, this was one of the go-to scapegoats for grandstanding politicians for nearly a decade. The fact that Columbine shooter Eric Harris was revealed to play it certainly didn't help matters (not only that, but he made a Doom WAD of his own called UAC Labs, which made it onto DoomWorld's Top 10 Infamous WADs list).
  • Multi-Mook Melee: Many of the custom "slaughter maps" and Nintendo Hard megawads are mostly made up of these, with some fights in the infamous Deus Vult map (maps 1-4 are parts of the main map, which is map05) or the ever fun "Go 2 It", which involves a brawl against several Arachnotrons and Cyberdemons. The infamous nuts.wad has so many enemies note  that on badly coded ports framerate slows down to a crawl, even if using a computer made 20 years after the original game. However, serious maps with that many monsters have also been made.
  • Multiplayer Difficulty Spike: When played in co-op mode, the games have extra enemies (including boss enemies like the Spider Mastermind and Cyberdemon) in places where they weren't there on even the hardest single-player difficulty.
  • Nameless Narrative: Proper nouns are never given for any character, as the only human of any consequence is Doomguy and there are no unique demon characters. The sole exception to this is when Episode 4 names Doomguy's pet rabbit "Daisy".
  • Nerf: In the PlayStation port of Doom, Revenants were nerfed considerably, having the speed of their movement and punches/missiles reduced by about half. Though in some compensation, they only fire homing missiles instead of mixing them in with straight shots. The player's Plasma Rifle also had its firing speed reduced by about half here, though it remained useful and able to reliably stunlock anything but a Baron and the bosses to death.
  • Nigh-Invulnerability: Due to how it's programmed, the iddqd cheat only makes you this rather than the complete invulnerability later games with a similar cheat would grant. The cheat makes the Doomguy invulnerable to anything that deals less than one thousand points of damage, meaning there are only two things in the unmodified games that can kill him in that state: telefrags, since they deal ten thousand points of damage (this is normally not a problem since monsters are programmed specifically to be unable to teleport in if the player is occupying their destination, though the spawn cubes of Doom II's MAP30 and voodoo doll shenanigans where one telefrags oneself are exempt), and the type of damaging floor used at the end of Doom E1M8, which is programmed to nullify god mode (since being damaged to below 11 health by that floor is how ending the level is triggered).
  • Night of the Living Mooks: The player fights marines who were killed by The Legions of Hell and now serve the demons. Their danger is not in their undead state, but rather, the firearms they carry and the hitscan bullets that they fire. The former human commando is especially fearsome.
  • No Body Left Behind: While this doesn't happen in the original PC versions, it does happen in the Game Boy Advance ports due to performance reasons.
  • No Fair Cheating: Using "-turbo" prints a chat message from time to time. In the original, and most ports of it, cheat codes are disabled entirely in Nightmare difficulty.
  • No OSHA Compliance: There are barrels of toxic waste strewn all over the place. And the pits of toxic waste, later lava, and blood. The Radiation Suit entry in the Doom II strategy guide calls this trope out almost word-for-word: "OSHA may not like it, but to get the job done, you're going to have to handle a little toxic waste."
  • Normal Fish in a Tiny Pond: The Barons of Hell. In later episodes, rockets, the Plasma Gun and the BFG can trivialize them. However, in the final level of the first episode (Phobos Anomaly), you will have no plasma cells and five rockets at best, so two Barons become fearsome bosses.
  • Nostalgia Level: The music in E2M2 is a remix of Wolfenstein 3-D's E2M10 music. Additionally, one of the Episode 1 maps was supposed to have some machinery in the shape of a swastika (only obvious when looking at it in the automap), though they were forced to change it before release.
  • No Swastikas: A map area in the original game was originally a swastika as a homage to Wolfenstein 3-D — this was changed in v1.4.
  • Nothing Exciting Ever Happens Here: The basis for the original game; the marine's Antarctic reassignment following his incident with his superiors. Sent to Mars to simply keep him out of sight and out of mind, he happens to be in the right place at the right time when things go south.
  • Not Afraid of Hell: Doomguy. It's Hell that is afraid of him.
  • Novelization: Four books based on Doom and Doom II (with the first two being actual novelisations of the game's storyline, such as it was). And two more based on Doom 3.
  • Nuclear Candle: The actual effect of the Light Amplification Visor is to brighten the whole map to the max level.
  • Number of the Beast:
    • The version of Doom released to coincide with the original release of Doom II is v1.666.
    • The first map of "Knee-Deep in the Dead" has 666 linedefs in The Ultimate Doom.
    • The original Doom engine used port 666 for its multiplayer.
    • In E1M8, killing both Bruiser Brothers will cause the star-shaped wall to lower and is internally tagged as '666'. Same for the wall to the exit after killing the Cyber Demon in E4M6 and the wall surrounding the exit after killing the Spider Mastermind in E4M8.

    O-Q 
  • Oddball in the Series: The two Doom RPG games for being RPGs in a shooter series.
  • Oh, Crap!: If Doomguy is hit by a particularly strong attack and survives it, such as a Cyberdemon's rocket, he's supposed to make this expression. It doesn't quite work as intended in the original release, however.note 
  • One-Hit Polykill: Shotgun can punch through whole columns of weak or damaged enemies in a single shot since any dying enemy immediately becomes a non-entity to the physics engine, transparent to all of the shotgun's multiple pellets.
  • One-Man Army: The eponymous Doomguy very quickly becomes this. After the initial invasion, he then proceeds to slaughter hundreds of thousands of hellspawn, so much so that he's literally too tough for Hell to contain, to the point where they all but tell him to get the Hell out. After returning to Earth, he proceeds to kill even more demons (in part to avenge his pet bunny Daisy).
  • One-Word Title: The original Doom, often stylized in capitals (DOOM).
  • The Only One: You play the lone space marine who was left on guard duty at the ship, now the only thing standing against the hordes of hell.
  • Only a Flesh Wound: Being a health-bar-based shooter, the game does this with tougher enemies and averts with weaker ones, which can be turned into mincemeat with hits from sufficiently powerful weapons - you can't do it with the pistol, chaingun, or either shotgun, but a rocket, either of the plasma weapons or punching them while under the effects of the berserk pack can do it.
  • Our Imps Are Different: Imps are the most common demons Doomguy will encounter; they typically resemble lean humanoids covered in spikes or bony armor. Their primary weapons are fireballs at long range and their claws at close range. Beginning with Doom³, they can also use their claws to climb on walls and objects. They're the lowest on the demon totem pole, with only former humans being lower; in combat, they're Fragile Speedsters who rely on mobility and agility to make up for their physical fragility.
  • Our Zombies Are Different: The zombies in this game are very humanlike, to the point where they wield guns instead of shambling with their bare mitts like your typical living dead.
  • Over 100% Completion: The game can tabulate a kill percentage above 100% on any level with an arch-vile in it, since arch-viles can resurrect dead monsters, except other arch-viles. A player routinely has to down the same enemy multiple times before concentrating fire upon the arch-vile itself, which raises the kill count above the installed enemy count. Also, the game's hardest difficulty (Nightmare) features respawning monsters and killing a monster after it respawns will count twice for the kill percentage, meaning that it is common for the kill percentage to exceed 100% in Nightmare runs.
  • Overdrawn at the Blood Bank: Doom was one of the few video games in the early '90s that demonstrated that 2D sprites can spill lots of blood, and some enemies can be gibbed when killed by high-powered weapons.
  • Painfully Slow Projectile:
    • Most monsters' projectile attacks move very slowly. Unless you're playing on Nightmare difficulty, where several enemy projectiles move at double speed.
    • The BFG-9000, no matter the incarnation.
    • Averted with the Cyberdemon, whose rockets are just as fast as yours.
  • Palette Swap: The game uses palette swaps mostly for changing the uniform color of different players in multiplayer mode (the green armor becomes indigo, brown and red for players 2, 3 and 4); however a variant of palette swap is used for one of the monsters: the Spectre is a Demon whose sprite's shape is replaced by a zone of transparent static.
  • Password Save: In the PlayStation and Saturn versions of Doom.
  • Path of Greatest Resistance: If a room is filled with bodies, you've already been there.
  • Permanently Missable Content: Some secret places are permanently closed off once you miss them (Episode 2 is especially guilty of this).
  • Planet Heck: The game showcases the archetypal example, with the player tasked with stopping an invasion of demons at their source, after fighting them off at a series of Mars bases.
  • Plot Coupon: The Blue, Yellow, and Red keys, when playing in single-player mode.
  • Physical Hell: Doom's entire plot revolves around the idea that teleportation experiments on Mars resulted in portals to Hell itself, cue The Marine.
  • Pocket Rocket Launcher: The Rocket Launcher has a 50-round magazine and handles like an assault rifle.
  • Popcultural Osmosis: The Imps use stock camel sound effects.
  • Possessing a Dead Body: The Former Humans are of this variety. They were Marines killed by the demons, which then took possession of their fallen bodies.
  • Power-Up: There are a variety of items that can give you an edge against the demons, including:
    • Backpacks, which double your ammo capacity for the remainder of the episode
    • Berserk, which lets you inflict devastating damage with your bare hands while also giving you a health top-off
    • Computer Area Maps, which fill in your map completely
    • Invulnerability, an Invincibility Power-Up (which also temporarily renders your vision in monochrome negatives)
    • Light Amplification Goggles, which grants you better vision in dim areas
    • Partial Invisibility, which makes enemies have a harder time aiming at you
    • Radiation Shielding Suit, which prevents damage from walking over hazardous terrain for a minute
  • Power Up Let Down: The Blur Artifact (partial invisibility) is detrimental against most enemies. Normally, enemies aim right at you, so it's not too hard to sidestep out of the way. Partial invisibility causes their aim to be offset to simulate how you're harder to target, which in practice makes it harder to dodge the projectiles by making their trajectory harder to predict. It's only beneficial when facing enemies with hitscan attacks since you can't dodge these anyway.
  • "Psycho" Strings:
  • Psychotic Smirk: The marine is rather passionate about battling Hell's hordes as, after a new weapon is picked up, the protagonist grins devilishly at the prospect of blowing away demonic forces with it. The effect is magnified if the face in the HUD is bloody from taking damage.
  • Punny Name: Several songs on the soundtrack, including but not limited to Kitchen Ace (And Taking Names) and Nobody Told Me About Id.
  • Quad Damage:
    • The Berserk Pack multiplies fist damage by ten times. For the rest of the level. You can gib weak mooks by punching them.
    • There's a (hopefully) intentionally crappy mod out there called All Hell is Breaking Loose! Among such things as flying demons that shout "Fuck you!" and flip you off when they die, the zombie soldier gib animation is replaced with them burning to death. This means that you can set someone on fire with a punch.

    R-S 
  • Railing Kill: If any monster is killed at a certain height above the player then it will push their corpse toward the player to achieve this effect for monsters near ledges, though it does result in a few oddities like Lost Souls and Cacodemons being pulled toward the player as they die.
  • Random Number God: Nearly every attack in the game, from both the player's weapons and demons' attacks, deals randomized damage, with the only exceptions being Splash Damage (where the amount of damage is determined by how close you or the monsters are to the centre of the splash damage source) and the launching hit of the Arch-vile's attack (which always deal 20 damage before the splash damage component is factored). The most extreme example is the Berserk Punch, with its damage ranging from 20 to 200 damage per punch - low enough to where it can fail to one-shot Imps and even Shotgunners, but high enough to potentially one-shot Pinkies and two-shot Revenants. Enemies' hitscan attacks, aside from the Arch-vile's, are additionally randomized where they shoot at, while the player's shotguns are subjected to random deviation with their spreads, and the Pistol and Chaingun will have their shots randomly deviate from the player's direct aim if they're held down to fire. Then each time an enemy is hit, it's completely random if they'll enter their "pain state" and get stunned for a split-second, with each type of enemy having a programmed "pain chance" that determines how likely it is that each hit triggers their pain state. This video explains how the random number generator works, while this video delves farther into enemy stats and shows the aspects that are randomized, while this video does the same for the players' weapons.
  • Ranged Emergency Weapon: The starter pistol in the classic games is a peashooter that won't be used for more than killing a former human or two until you get the shotgun, and after that to snipe enemies at extreme distances. As soon as you get the chaingun, you're unlikely to press 2 on purpose for the rest of the game or chapter, as it does everything the pistol does but better and faster.
  • Rated M for Manly: Admit it, you've always wanted to kill demons with your bare hands.
  • Real Is Brown: The original game was noted for its "realistic" graphics, back in its day. Sure, plenty of levels go for muddy browns and greys, not helped by the generally dim lighting, but the palette has plenty of very saturated blues, greens, oranges, yellows and reds. The starting position of the first level of the first episode makes the deep blue floor very evident.
  • Real Men Wear Pink: The original berserker-packin' man-and-a-half's reason for blowing up hell? The demons killed his pet bunny, Daisy.
  • Reassigned to Antarctica: The Doomguy in the original two games assaulted a superior officer who ordered him to fire on civilians. Rather than a court martial that would make them look like monsters if the reason for it got out, they decided to assign him to Mars — a barren rock whose only notable features were scientific outposts on its moons, and which was never expected to see any sort of action. It turns out to be a blessing in disguise, as he's the only one able to take on the demons when the invasion happens.
  • Reassignment Backfire: According to the help file included with the registered version of the game, the Marine was relocated to Mars, a backwater dustball whose only notable features were scientific outposts on its moons, in lieu of a court-martial for striking a commanding officer who had ordered him to fire on civilians. No, they didn't just make that up for the novel. He, of course, went on to save the world from the forces of Hell over the course of two games. And, as revealed by Doom Eternal, would go on to wage war against Hell for millennia.
  • Recycled Soundtrack: The music heard in the second level of Episode 2, "The Demons from Adrian's Pen", is based on one of the secret level themes from Wolfenstein 3D.
  • Red Eyes, Take Warning: The Spider Mastermind (AKA Spiderdemon) has glowing red eyes. It also has a chaingun that will chop you to pieces if you give it a clear shot at you. The smaller Arachnotrons are a downplayed instance, normally featuring blue eyes, but which flash red with every shot they take at you with their built-in plasma gun.
  • Red Filter of Doom: Throughout the classic games, when you pick up the Berserker Pack, your screen will turn red, you'll be restored to 100 health if you were below that and your fists become more powerful than a shotgun for the rest of the current level.
  • Red/Green Contrast: Doomguy is a Space Marine who wears green armor and defends Earth from The Legions of Hell. His demonic opponents tend to be predominately red, and his adventures typically take him to Mars, the Red Planet.
  • Red Shirt: The instruction manual explains that Doomguy didn't come alone to Phobos - he arrived with a whole team of marines, who entered the base to investigate while he guarded the perimeter. The demons have already killed them all by the time the game begins; you can find their corpses strewn about the first level.
  • Red Sky, Take Warning: There's a red sky in the last third or so of the games. The third episode of the original game, Inferno, set in Hell itself, has a fittingly blood-red sky. The fourth episode, Thy Flesh Consumed, has a mostly sunset-yellow sky tinged with red.
  • Religious and Mythological Theme Naming: Excluding the secret level, every map in the fourth episode is named after a phrase from the Bible, as is the episode itself ("Thy Flesh Consumed", a phrase from Proverbs 5:11).
  • Remixed Level: Doom seems to take you back to the first level of Episode 3 for its secret level, and it plays out much the same...that is, until you enter the exit teleport and the walls come down revealing an arena reminiscent of Episode 2's boss level — complete with a pissed off Cyberdemon! And that's only the beginning...
  • Respawning Enemies: The Nightmare difficulty has this as part of what makes it so hard, where any enemy that leaves a corpse would get back up after a random interval that could be anywhere from eight seconds to five minutes (usually closer to the former).
  • Resurrection Sickness: Normally, enemies have a reaction time of 8 tics (frames) between seeing you and firing, and on Nightmare Difficulty their reaction time is 0 tics.
  • Ret-Canon: The Doomguy in the cellphone-only Doom RPG series is related to B.J. from Wolfenstein 3-D.
  • Road Runner PC: The Doom marine was intentionally faster than normal monster movement and could be made faster with a command line option. What wasn't intentional was strafe-running (+40% speed boost), and wall-hugging (massive speed boost).
  • Roaring Rampage of Revenge: At the end of episode 4 in The Ultimate Doom it is revealed that the Doomguy's reason for killing all the demons was to avenge his pet rabbit Daisy, whose head you see on a spike at the end of episode 3
  • Rocket Jump: Ur-Example in first-person shooters. There's no vertical lift, but it does toss you around. One secret in the third episode (leading to its hidden level) was specifically designed to require a rocket jump... though it can be reached just by strafe-running.
  • Rocket-Tag Gameplay: Given the Health/Damage Asymmetry, deathmatches between players are naturally this. Even the player's humble Shotgun will two-shot another player at the default 100% health and no armor, and the stronger weapons will kill other players even faster, to say nothing of how overkill the BFG is. Doom II would push it even farther with the Super Shotgun, a weapon able to one-shot at close range while being Hitscan (meaning it can't be dodged unlike the stronger projectile weapons).
  • Scenery Porn:
    • Try playing a map pack that requires a limit-removing source port and you're bound to get one of these. With the removal of the vanilla engine's notoriously strict mapping limitations, one of which closes the game entirely if exceeded, map creators became free to add extensive details to the architecture as well as huge sprawling open areas in their maps, resulting in stunning scenery if executed properly.
    • The Back to Saturn X series has gorgeous maps and impressive detail... designed to run under the vanilla engine, within its mapping limits as noted above. The trickery used to make bridges appear 3D as well as texture cheats to create the illusion of sloped or curved arches are incredible.
  • Schizophrenic Difficulty: Episode 4 of Ultimate Doom does not remotely have any sort of difficulty curve. It immediately hits you with the vicious one-two punch of Hell Beneath and Perfect Hatred, maps both far harder than anything else that came before in the first three episodes and arguably harder than anything in Doom 2. If the player is able to survive them, they are followed by Fear (if you took the secret exit out of Perfect Hatred) and Sever the Wicked, maps that have a high octane start surrounded by enemies but are otherwise much more manageable. Then you get Unruly Evil, a very short and pathetically easy map, especially if you're not Pistol-starting. The difficulty climbs a bit after with They Will Repent, though it's nothing noteworthy difficulty-wise. The difficulty then spikes way back up with Against Thee Wickedly, a map that often tops players' map difficulty rankings for the first two Dooms and ends with by far the most difficult Cyberdemon encounter in either Doom 1 or 2, which would have made for a very fitting final map. However, it's not the final map, and is instead succeeded by And Hell Followed, an easy laidback map that's barely above Unruly Evil in difficulty, while the episode then finishes with Unto the Cruel, a map of mediocre difficulty that ends in yet another anticlimactic Spider Mastermind fight.
  • Science Is Bad: The game is based on the premise that teleportation is a literal contact with Hell. Half or more of the demons are cybernetically augmented. On the other hand, experimental weapons tend to save the day.
  • Second-Person Narration: The narrations at the end of each episode are in the second person.
  • Secret Level:
    • Each Episode in Ultimate Doom has a secret map accessible via a secret exit in one of the Episode's maps:
      • Episode 1 has Military Base, which is accessible via a secret exit in Toxin Refinery. It is a conventional map, just being a bit more difficult than other Episode 1 maps, but it does notably contain the first teleporting monster ambush in the game, though this trap was replaced with a normal Monster Closet ambush in all of the '90s console ports.
      • Episode 2 has Fortess of Mystery, which is accessible via a secret exit in Command Center, though its accessibility varies in early console ports; in the Super Nintendo port the secret exit to it was moved to Refinery, in the Playstation and Saturn ports the secret exit to it was moved to Spawning Vats, and it wasn't a secret map in the Jaguar, 32X, and GBA ports, instead being the final map of those ports. As for the map itself, it's notorious for its overt simplicity, consisting of just two plain rooms, one with four Barons, and the other with ten Cacodemons, with its purpose being to show off monster infighting.
      • Episode 3 has Warrens, which is accessible via a secret exit in Mount Erebus, though the map was removed in the Jaguar, 32X, GBA, Playstation, and Saturn ports (but interestingly it was retained in the SNES port). This map has the gimmick that it initially appears the player was sent back to the Episode's first map, Hell Keep, is exactly the same as that map up until the secret near the end, which no longer has a Rocket Launcher, the first signal that something isn't right. Then when the player steps onto the "exit" teleporter, the walls come down to reveal a large arena with a Cyberdemon, and then the player must backtrack through the map, with more rooms opened up containing more dangerous enemy encounters than the original map had.
      • Episode 4 has Fear, which is accessible via a secret exit in Perfect Hatred, though the map was removed in the Playstation and Saturn ports, and of course doesn't exist in the other console ports that don't have Episode 4 (the SNES, 32X, Jaguar, and GBA ports). It's a banal conventional map that is noticeably much easier than the two Episode 4 maps preceding it, with its only noteworthy feature being its symmetrical design.
    • The Playstation and Saturn ports had a few of their own exclusive secret maps that were never seen in the PC version or any of the other ports:
      • In the Ultimate Doom portion of these ports, there's a new secret map called The Marshes, which is accessible via a secret exit in Twlight Descends, which itself is a new map exclusive to these ports. This map is a large arena resembling, as the name implies, a marsh-like area, containing a Cyberdemon and a handful of other mooks.
      • In the Doom 2 portion of these ports, the two secret Wolfenstein maps were replaced by two new secret maps:
      • The first such secret map is The Mansion, accessible via a secret exit in Suburbs. It is mostly a conventional map with nothing out-of-the-ordinary gameplay-wise other than a tricky teleporter maze puzzle, but the map does visually standout for its depiction of a Resident Evil-like mansion, taking strong advantage of the ports' colored lighting to create an unsettling atmosphere, with it especially standing out compared to the drab Doom 2 maps.
      • The second such secret map is Club Doom, accessible via a secret exit in The Mansion. The map starts out looking unsettling, being a pitch-black area only lit by a row of candles going into an ominous-looking building. But upon entering the building and turning the corner, loud rave music starts playing as the player enters a strobe-lit nightclub area full of Revenants on a dance floor and in go-go cages.
    • The original Xbox port, while otherwise mostly a 1:1 port of the PC original, has its own unique secret map in Episode 1: Sewers, accessible via a secret exit in Hangar. This map was created by one of the ports' developers, David Calvin, back in 1994. Otherwise, there's nothing noteworthy about it other than being a banal 1994 WAD that really shows its age. This map was not included in any other port but is available as a standalone WAD online if one wishes to play it. Interestingly it was also available several years earlier in Maximum Doom, an official WAD compilation from 1995 that contained nearly 2000 WADs downloaded from the internet, as well as being included in the many other unofficial shovelware WAD compilations of the '90s.
  • Sensory Abuse: An infamous genre of WAD, referred to as Terry WADs after the troll who made the first examples, is built on this. These WADs play like normal until you activate a certain switch or linedef, at which point you're bombarded with ear-splitting noises, flashing lights, and text that describes anally raping the reader.
  • Sequence Breaking:
    • Straferunning is just one example of sequence-breaking tricks.
    • Jumping isn't possible in the original Doom, but many later source ports allow it. On some maps, this makes it possible for the player to jump onto platforms they aren't supposed to be able to reach yet (or even at all).
  • Set a Mook to Kill a Mook: A vital survival technique in the classic Dooms, especially in levels with more monsters than you can shake a boomstick at.
    • If an enemy damages another enemy in any way, they will engage each other to the death unless angered by the player or a different foe. Infighting has some rules to it, such as monsters of the same type cannot damage each other with their projectiles unless they use a hitscan weapon, and when a monster is damaged, they'll have a randomised "targeting threshold", i.e., a period of time where they'll ignore damage from the player/other monsters while engaging the player/another monster they were initially damaged by.
    • Some of the levels even outright encouraged the player to exploit through design, some examples of which:
      • The first area of E3M1 didn't have enough ammunition to kill all the Beef Gates. It was to punch them to death or get them fighting each other. Since Imps and Cacodemons both had ranged attacks, getting them to hit each other was relatively easy. Then the retaliation started...
      • E2M9, the secret level in the second episode, had two rooms. One with Barons of Hell, the other with Cacodemons. Again, the trick was to get them to fight each other, and then manoeuver for survival. Lampshaded in the novels.
    • Lost Souls behave differently with in-fighting; they will make at most one attack when damaged (but can still exchange blows), and then resume attacks on the player. This gives them a rather cute personality since it will frequently happen that one will accidentally charge into another, causing the victim to bite it back in retaliation and appear to argue with each other before one eventually misses and they both resume their attack on the player.
  • Shareware:
    • One of the most well-known examples, Doom is probably the one title above all others that destroyed forever the "shareware is shareware because it's nowhere near good enough to sell at retail" myth. It was the first shareware product ever to be reviewed on the main pages of British PC Format magazine, instead of being relegated to the shareware section.
    • Carmack has said in a 20th-anniversary interview that shareware was actually not such a great fit for Doom. Not because of any problem with the strategy itself, but because the game was such an obvious generational leap forward in game technology at the time, it literally sold itself, without the need for any marketing gimmicks.
  • "Shaggy Dog" Story: You fight through hordes of monsters, including literally going to Hell and back... only to find on your return to Earth that the demons have already invaded. And their first victim was Daisy, your pet rabbit.
  • Shoot the Medic First: In ZDoom, it is possible to create enemies that can resurrect fallen foes via Decorate. Death for these guys should be a top priority.
  • Shoot the Shaggy Dog: The original screws you over twice:
    • First, after defeating the Barons of Hell in the final level of the first episode, the only way out is through the teleporter... which takes you to Hell, where you're immediately overwhelmed by monsters and die (the coding in that room ends the level once you reach 11 HP or lower). The debriefing text really drives it home: "Once you beat the big badasses and clean out the moon base, you're supposed to win, aren't you? Aren't you? Where's your fat reward and ticket home? What the Hell is this? It's not supposed to end this way!"
    • And of course, the end of episode three. The Space Marine escapes from Hell and returns to Earth... only to find that the demons he had been fighting have already invaded. Cue the sequel.
  • Short-Range Shotgun:
    • The original pump-action shotgun has a modest spread that is entirely horizontal (i.e., the pellets all connect in a straight left-to-right line) that will allow a good amount of its 7 pellets to hit at long distances, to where it can even be used as an effective sniping weapon in a pinch.
    • The SNES port combined all seven pellets into one uber-slug, meaning it was even worse for crowd control but game-breakingly effective as a predecessor to the Sniper Rifle.
  • Shout-Out:
    • On the source port side, ZDoom has the developer's console cheat "anubis". Typing it in and pressing enter results in every monster in the game fleeing at the sight of you. Why? Because the message displayed when you hit enter is QUAKE WITH FEAR. Typing "anubis" again and hitting enter deactivates the fear effect with the message "No more Ogre Armor".
    • In the film, Dwayne Johnson actually had to fight to keep the "BFG" reference. There's also Pinky (who gets chainsawed), a Hellknight, and Reaper saying, "Hell on Earth".
    • Episode 4 of The Ultimate Doom and all the levels within, excluding the secret one, have names based on biblical verses.
    • E4M1 of The Ultimate Doom has the Nine Inch Nails logo inscribed in a secret area. This was however removed in the 2019 Unity ports to avoid trademark infringement.
    • The penultimate difficulty level is named "Ultra-Violence".
  • Sickly Green Glow: Radioactive nukage glows a vivid emerald and damages Doomguy for as long as he's standing on it. You need a radiation shielding suit to cross over it safely. There are barrels filled with the stuff, and if shot at, they explode.
  • Shotguns Are Just Better: The first game has a simple shotgun as the second weapon you'll likely get. It does a good amount of damage, especially at short range, and the ammo is extremely plentiful, making it perhaps the most frequently used weapon in the game.
  • Sigil Spam: The UAC logo from door to blue carpet and even screensaver.
  • Sinister Nudity: The hellspawn, however, from imps up to and including the Cyberdemon, go about unclothed as they launch fireballs and rockets at the player. Only the Revenants have tattered clothes, while even the vaguely humanoid Arch-viles traipse about naked.
  • Skeleton Key: There are skull keys that are literally just skulls. Like keycards, they come in three colors: yellow, red and blue. In the official games, they're interchangeable with keycards of the same color; the Boom source port allows users to make doors that require specifically a skull key or a keycard.
  • Slasher Smile: The Doomguy's face on the Expressive Health Bar gives a menacing smile when you pick up a new weapon, making it clear that he's excited to try out his new toy on the Legions of Hell.
  • Slave Mooks: The zombified soldiers have become slaves to Hell. In the first game and the next two in the series, they're slow-moving, inaccurately-firing zombies that seem to be nothing more than animated and armed corpses
  • Sliding Scale Of Silliness Vs Seriousness: The first four games are generally pretty serious (Doom 64 and Doom³ more so), but have bouts of goofiness and Black Comedy here and there. Doom (2016) and Doom Eternal, in comparison, are much sillier, with tongue-in-cheek plots involving an Obviously Evil MegaCorp fracking hell for resources, largely comedic codex entries, many cases of Ascended Meme, and some pretty out there easter eggs. Even the Doom Marine has his moments.
  • Smoldering Shoes: The Cyberdemon's death animation in the original series has it explode, leaving just its hooves.
  • Sniper Pistol: The Trope Maker. If you pause for about a second in between each pistol or chaingun shot, it will have perfect accuracy. But in an era where headshots didn't exist, this was rarely a viable tactic for killing anything but zombies and imps.
  • Sole Survivor: The Marine is the sole survivor of his unit. Unless you play Co-Op.
  • A Space Marine Is You: Possibly the Ur-Example, although most of the cliches are only found in the backstory from the game manual.
  • Spider Tank: The boss of Episodes 3 and 4 is the Spider Mastermind, a large robotic monster whose organic brain is controlling the mechanical rest of the anatomy. Its weapon is a super-chaingun.
  • Splash Damage: The always venerable rocket launcher, along with the classic Exploding Barrels. Interestingly, the BFG, the biggest gun in the game, does not deal blast damage in the traditional sense, though; it instead fires a cone of invisible beams (from the player, not the projectile) in the direction the main projectile was fired in when it hits anything.
  • Splash Damage Abuse: Rockets have reasonable horizontal splash range upon detonation but do damage in an infinitely tall vertical cylinder due to how the engine works. An enemy that is close to an explosion but very far beneath or above it will still take damage. Demonstrated in this video.
  • Standard FPS Guns: Fists, Chainsaw, Pistol, Shotgun, Chaingun, Rocket Launcher, Plasma Rifle, BFG. Doom was very important in creating and popularizing this one.
  • Stat Overflow:
    • The Soul Sphere adds 100% health on top of the player's current percentage: at 44% health + Soul Sphere = 144% health.
    • The Mega Sphere, pushes both health and armor up to the fixed value of 200%.
    • Health and armor bonuses add health/armor by 1% increments that surpass 100% health/armor.
  • Status-Buff Dispel: While a God Mode cheat exists, there also exists a damaging floor type that can nullify it: Type 11, first introduced at the end of E1M8: Phobos Anomaly. Type 11 damaging floors inflict 20% damage per second (split between health and armor, if the player has any) and end the level when the player's health is at 10% or below. Telefrags can also bypass God Mode to One-Hit Kill the player in MAP30 of any Doom II-based WAD.
  • Status Line: It displays the protagonist's Character Portrait and all of the time-limited status effects (such as invisibility, invulnerability, and infrared goggles).
  • Stealthy Mook: The Spectres are partially invisible versions of the pink Demons. This ability is not true invisibility (except in dark rooms) but is enough to trip up a player if they're not totally observant.
  • Stock Sound Effects: Almost everything, from the monster roars to the launch sound of the monster spawn cubes in MAP30, thanks to id licensing sound FX from the Sound Ideas library. This is why all, or nearly all, of the FX used in Doom sound familiar to movie buffs; they've been used in many movies and TV shows, both before Doom and since. In fact, one of the stock sounds is known today as Doom Doors.
  • Stone Wall: The Baron Of Hell isn't much of an offensive threat, since its attack consists of just throwing a single fireball in a telegraphed manner, and they don't move around fast either. However, with 1000 HP and a very low pain chance that makes even the Plasma Rifle unable to reliably stunlock it, it's very resilient compared to anything short of a Cyberdemon and Mastermind. Barons are often used by map makers to take advantage of this capacity, with groups of them being placed in fights to corral players into disadvantageous positions as they're too bulky to just blow through, to act as durable shields for more pressing threats like an Arch-vile, or to act as "doors with health" that block players from accessing areas without expending an unhealthy amount of ammo and time.
  • Strange Secret Entrance: Some of the hidden levels in the series are like this. For example, getting to one secret level required you to blow yourself off a ledge by firing your rocket launcher into a wall at point-blank range.
  • Stupid Evil: The demons will ignore Doomguy to attack their allies if they are accidentally hit in the back.
  • Summon Bigger Fish: If you can get powerful monsters to fight each other or mow down cannon fodder, you can save yourself a lot of trouble. There is even a secret level in Episode 2 with this premise: In the room you start with there are half a dozen Barons of Hell. In the next room are a dozen Cacodemons. The best survival strategy involves running from room to room, allowing the monsters to mix and get caught in each other's crossfire, which will make them turn on each other as long as you aren't foolish enough to draw their attention.
  • Supernatural Gold Eyes: Picking up invincibility (or turning on God Mode) turns the Doomguy's eyes gold.
  • Super Title 64 Advance:
    • The official Windows of Doom was named Doom95 as it was developed for Windows 95 to promote the operating system as a gaming platform.
    • The PlayStation port of Doom has the subtitle "Custom PlayStation Edition".
  • Surreal Horror: One thing that stays consistent throughout the franchise is that Hell is really Goddamn weird. The laws of physics as seen in our reality don't seem to apply most of the time, and the areas you're fighting through can suddenly shift into another shape entirely. And some of the surfaces are made of spinal columns and human faces.
  • Suspiciously Cracked Wall: There are wall textures noticeably different to draw attention to secret doors, sometimes misaligned or bordered but often with conspicuously damaged wall segments such as this, this or this. Played straight when the wall is set to open on damage, meaning you have to physically attack the wall to make it open.
  • Suspicious Videogame Generosity:
    • E2M8 gives you four Soul Spheres and a massive amount of every ammo type you're certain to have at that point. Not so much "generous", though, since the doors to them close behind you, and the Cyberdemon is waiting in one of the far corners of the map beyond, so you can only safely grab everything from one or two of the four rooms (depending on which one you pick first).
    • Cyberdemon battles are almost always preceded by you finding a massive supply of rockets and a rocket launcher. Ironically, this is actually not a very good way to handle them; Cyberdemons and Spider Masterminds only take damage from the direct hit of a rocket, not any splash damage from the explosion. The Plasma Rifle and BFG are usually recommended instead.

    T-Z 
  • Tactical Door Use: While monsters can open many doors, there are several ones they cannot (particularly ones requiring keycards or opened by switches, although these are not the only examples). Similarly, players can quickly open a door, shoot into the next room and close the door again as a means of slowly picking off opposition from behind cover (or inducing monster infighting as the monsters end up accidentally hitting their buddies with fireballs).
  • Tactical Suicide Boss: Due to how enemies are coded to react to barrels exploding and hurting them, it is possible to trick the Barons that cap off the first episode into fighting one another, despite code designed to prevent this, by having one damage a barrel and then the other destroy it while the first Baron is within its blast radius. Early versions of the game were even worse, as the way the code worked meant that it was also possible to trick a Baron into infighting with itself via barrel, causing it to swipe at the air in random directions and literally tear itself apart.
  • Tagline: "Doom...where the safest place is behind a trigger!"
  • Take That, Audience!: The ending text for the PlayStation and Saturn ports tells the player they can "retire to a lifetime of frivolity".
  • Tank Controls:
    • Controlling the original game with only the keyboard or only the mouse defaults to this, though with the ability to strafe by holding a modifier key that changes your turning controls into strafing ones while it's held. Using both at once allows for separate turning and strafing.
    • Also, the case for the SNES port; like the DOS original there's a button to read the turning controls as strafing, but it's impossible to turn and strafe at the same time in this version.
    • The default setting for the PlayStation and Saturn versions, as well. You can change the controls, although it's not very extensive.
  • Tech-Demo Game: This game and Wolfenstein 3-D were made when Carmack decided to one-up Looking Glass Studios and their Ultima Underworld series' 3D visuals. Carmack claimed he could make a faster renderer, not a better one. Ultima Underworld and System Shock were far more punishing on the hardware of their era than even Doom was.
  • Tele-Frag: Just like "frag", it was also first coined in Doom multiplayer matches. Some Doom levels allow you to telefrag monsters (e.g., E4M2 in The Ultimate Doom). Telefrags also ignore whether the telefragged is invulnerable or not and just outright splat them. To be exact, "invulnerable" (whether by Power-Up or by God Mode cheat) means "immune to attacks scoring 1000 Hit Points or less of damage". A telefrag is the only source of damage to surpass that, doing 10,000 HP damage.
  • Teleportation: This is the plot of the original game, and it's the reason why many levels feature miniature teleporters (marked as glowing red tiles with pentagrams drawn in them).
  • Teleporter Accident: A teleporter breaches hell in the backstory. The demons took notice and decided to pay humanity a "friendly visit".
  • Teleporting Keycard Squad: More often than not, you can expect to find a horde of demons swarming upon you when you pick up a keycard.
  • Teleport Spam: It is possible to make an invisible teleporter that works only for monsters.
  • Ten-Second Flashlight: Downplayed in the classic games with the Light Amplification Visor, a pickup that turns your whole view into fullbright. It only lasts two minutes, but given the pacing of the games, that tends to be long enough to explore the dark sections of the maps the LAV appears innote . Curiously, it's the non-permanent powerup with the longest duration in Doom.
  • There Is No Kill Like Overkill: Overkilling weak enemies is encouraged by the game, as do enough overkill damage to a zombie or Imp (by reducing them to negative health equivalent to their base HP in a single hit) and they'll go through a satisfying death animation of them exploding apart, referred to as gibbing. Doom Guy himself can also be gibbed by especially powerful attacks.
  • This Is Gonna Suck: The hardest difficulty setting is Nightmare!, featuring faster monsters that respawn shortly after being killed, and most cheat codes are disabled. The only advantage you have is that enemies that drop ammo drop more than normal. When selecting it, the game asks "Are you sure? This skill level isn't even remotely fair."
  • This Looks Like a Job for Aquaman: Normally the Partial Invisibility powerup is a detriment, as the erratic randomized firing it causes in enemies makes their projectiles a lot more difficult to dodge as you can no longer anticipate where they fire. Against enemies with hitscan attacks however, as you can't dodge their attacks to begin with except by praying that they decide to miss, the erratic firing will cause them to miss you a lot more often and save you from a lot of otherwise unavoidable damage. As such, when against a large number of hitscanners, especially Chaingunners, Partial Invisibility becomes immensely useful. note 
  • To Hell and Back: Episode 1 ends with the Marine being killed and sent to Hell as a result. He then fights his way out of Hell back to Earth. On top of that, megawad Sigil (conceived as an unofficial "Episode 5" to Doom created by John Romero) has Doomguy being sent back to and fighting his way out of Hell again.
  • Tower of Babel: This is the name of the final map of the second episode, and that is where you fight the Cyberdemon, quite possibly the toughest monster in the entire series. Unusually, no climbing is involved, but with each mission you complete in Episode 2, the Tower is being built, part by part, until it reaches the top when you get close to it.
  • Toxic, Inc.: Never mind the demons from Hell, the UAC cannot be doing anything good for the Martian environment with all the deadly radioactive waste they have lying around. As the DOOM Guy himself notes in the Doom comic:
    "Even if I personally stop this alien invasion, what kind of planet will we be leaving to our children?"
  • Trope Codifier:
    • For the FPS genre. Until about 1998, when the genre shifted to full 3D with games like GoldenEye (1997) and Half-Life, they weren't even called "first-person shooters", but were instead "Doom clones".
    • The rude, manly space marine has become ubiquitous since then.
    • The "crate maze", as first seen in E2M2: Containment Area, has also become an FPS cliché. It originated as a good way to have a large area without overtaxing the engine.
  • Trouble Follows You Home: The original game ends on this note. You've just returned to Earth after literally going through Hell, only to find that Hell has broken loose on Earth, which leads to the events of Doom II.
  • Unbroken First-Person Perspective: As with other classic shooters like Wolfenstein 3D, this game pre-dates the tendency to break up gameplay with cutscenes, so the entire game is from Doomguy's perspective. The only things that could be considered breaks in perspective are text screens appearing at the end of each episode, which are narrated to the player in Second-Person Narration.
  • Underground Monkey: The Specters, which are similar to the standard Demons but have a partial Invisibility.
  • Unending End Card: The Sega 32X port has a credit roll, followed by a simple DOS prompt. If you instead completed 16 levels in a row, it follows the Doom II style ending which is also unending but at least cycles through the monsters and their death animations. In the case of the former, the game's manual incorrectly states the player will be cycled back to level 1.
  • Unexplained Recovery: At the end of the first game's first episode, you enter a teleporter that takes you to a pitch-black room with a special damaging floor and many monsters. As soon as you are reduced to 10 health or less, the level abruptly ends, with the implication that you died. However, the end text itself remarks how you wake up in Deimos, alive and unharmed but weaponless. Since it turns out that the entire moon of Deimos has been pulled into Hell, a common explanation is that you died and were sent to Hell... but if that's the case, why would you have a pistol and 50 bullets when you first materialize? The novelization by Dafydd ab Hugh and Brad Linaweaver says that Taggart (the Doomguy in this version) arrived naked and weaponless but found some weaponry. Maybe something similar happened offscreen?
  • Unintentionally Unwinnable:
    • E2M4: In version 1.1, approaching the yellow key, retreating to a different room, and returning causes the crushing ceiling to be permanently lowered, sometimes blocking access to the key. That version forgot the original ceiling height whenever the crusher stopped.
    • In E3M9 (Warrens), it is possible to lock yourself out of the first room by pressing the button to lower the first door in the level and then quickly running through the door before it closes. This will prevent you from beating the level.
  • Unique Enemy: The PlayStation port of the original game features a single translucent Cacodemon that's locked in a cage in the level Tenements. This is most likely an error, however, since translucency is a flag that can be set to any monster, but is only used to create the Spectre enemies.
  • "Untitled" Title: The levels "Fortress of Mystery" (E2M9) and "Hell Keep" (E3M1) have the music track "Untitled", possibly because "MIDI Version of Mouth for War" was too cumbersome and opened the door for litigation.
  • Unwinnable by Design: Subverted in the final map of the first episode. The hero is teleported into an inescapable pitch-black room surrounded by demons where he is torn to shreds. Many players repeatedly attempted to fight their way through the demons or find their way out of the darkness, wondering if there was a different ending. This is a subversion because the hero is SUPPOSED to die, and in fact that's the only way to complete the episode.
  • Updated Re-release:
    • The Ultimate Doom added no new monsters or weapons (not even the new ones added in Doom II), but a new episode to the original game. It was basically an excuse to get Doom, formerly distributed as shareware, sold in retail stores.
    • The Xbox LIVE Arcade version of The Ultimate Doom and Doom II has higher resolution graphics and Gravis UltraSound music, online multiplayer, and a new 9-level expansion for Doom II. These treatments were also added for PlayStation Network's Doom Classic Complete compilation along with the additions of Final Doom and the Master Levels.
    • The 2019 DOOM Enhanced editions of Doom I and II for PlayStation 4, Xbox One, Nintendo Switch, and mobile devices, after multiple patches, feature the ability to officially play these games in 60 FPS, added a new weapon wheel for weapon selection, split-screen multiplayer, and the ability to download curated and compatible mods from Bethesda.net, among them being Final Doom, No Rest for the Living, and SIGIL at the comfort of your favorite console/handheld/PC. This version later made its way onto PC as well on Bethesda.net and later Steam, GOG.com, and Epic Games Store, with the ability to add in your mods like in the mobile version. Another update later added 16:9 widescreen presentation, doubles the game's original resolution, features variable frame-rate options for supported devices, toggleable V-sync (when available), gyro aiming controls for Switch/PlayStation 4/PC with DualShock 4 controllers, a new Ultra-Violence+ difficulty, revamp the deathmatch multiplayer, and support for mods that uses DeHackEd.
  • Vague Hit Points: Enemies have Hit Points, as seen when looking at the source code, but there's no way to measure it in the regular game, instead the player can only remember how many hits of each weapon it takes to take down specific enemies.
  • The Very Definitely Final Dungeon: The second episode has the final level, "Tower of Babel", being actively constructed during the Marine's battle across Deimos.
  • Victory Fakeout: The Episode 2 level "Halls Of The Damned" has a fake exit, which has an exit sign and door just like a real one, but flipping the switch instead causes some walls to open and monsters to ambush you.
  • Visible Invisibility: A weird example: The invisibility sphere (more accurately named "partial invisibility" in the game) turns you into a sort of static outline. As such, you're not completely invisible to monsters - some may take a while to realize you're in front of them if you don't fire a weapon, and once a monster is aware of you, they'll fire off projectiles in your general direction rather than directly at you. The weird part is that it doesn't prevent monsters from seeing you but just makes their aim worse and has no effect on monsters with no ranged attacks.
  • Wake-Up Call Boss: The Cyberdemon, first appearing as the boss of the second episode. If you haven't learned to strafe and circle-strafe effectively yet, you stand no chance whatsoever against his rocket missiles.
  • Walk on Water: Doom was one of the first FPS games to actually include water and other liquids, but, as a side effect of its not-quite-3D engine, the water is still just a regular floor with an animated texture attached, meaning Doomguy can run across it just as well as he can with solid ground.
  • The Walls Have Eyes: Some wall sprites have moving walls of faces staring at you, and in later episodes/levels of Doom the switches are now stone heads whose eyes glow when you activate them. Other switches are just eyes protruding out of fleshy patches, closing when activated.
  • The War Sequence: Custom levels pitting the player against massive hordes of enemies (called "slaughter maps") are somewhat popular amongst the Doom community. The official Doom levels have a couple of their own as well, perhaps most (in)famously E4M2, "Perfect Hatred".
  • We ARE Struggling Together: Aside from being generally united against the player, the different species of monsters comprising the legions of Hell generally don't like each other, and while they'll attack you on sight, they'll be just as likely to attack any of their erstwhile "allies" at the slightest provocation (read: an errant fireball).
  • Who Forgot The Lights?: The PlayStation version deliberately has much darker lighting than the PC original, and when coupled with the eerie ambient soundtrack by Aubrey Hodges, it invokes a Survival Horror atmosphere.
  • With This Herring: Hand waved in the first couple of Doom games, where you initially do battle with the legions of Hell while carrying a single pistol. This is explained by the Excuse Plot saying that you were a sentry stationed outside the base while everyone else went in to find out what happened. Naturally, all those people with the huge guns got killed and you're the only one left. This does not come off as being particularly convincing.
  • Wrap Around: The map space will "wrap around" when reaching the borders, though no official map ever extends this far. This can be seen using no clipping; running in one direction away from the game world will eventually result in the player approaching it again from the other side. Player-made maps can take advantage of this though a level of such size can cause issues in some ports of the game. Additionally, strange effects occur at the "border" of the map space, notably with monster pathfinding not considering the open border of the map space to be a valid pathway.
  • Writing Around Trademarks: A peculiar example for Freedoom. As the game source code is free and open source while the graphics and audio assets aren't, Freedoom replaces the remaining assets with copyright-friendly ones, and are made free and open-source.
  • Your Head Asplode: In the PS1 and Sega Saturn versions when you get gibbed, the status bar face explodes rather than being all caved in and dead like a normal death. The 3DO version explodes the face no matter how you die.
  • Your Princess Is in Another Castle!:
    • In Episode 2, Mission 6, "Halls of the Damned", you go through a long corridor, up to a room with an "Exit" sign and a switch, that when you throw the switch the floor collapses into a room with a whole bunch of nasties; it was a trick to make you think it's the end of the level.
    • Episode 3's secret level "Warrens": it's an exact copy of the episode's first level, "Hell Keep", right down to weapon and monster placement, except significantly easier as you start with more than just the pistol. When you reach the end of the level, the teleporter doesn't bring you to the stat counter - it drops a bunch of walls, revealing new areas filled with new monsters - such as the Cyberdemon standing directly in front of you.
  • Zombie Apocalypse: The zombies are undead foot soldiers (a few pistol shots can do one in permanently), still using the firearms they had been carrying in life.

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BFG 9000

Doom (2016)'s version of the legendary Trope Namer. Which is able to clear out entire rooms of demons at once

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