History VideoGame / DOOM

* LongSongShortScene: The song "At Doom's Gate" is only played for the first map of the first episode, and it's a very short map.

** If lesser enemies (or players in Deathmatches) were hit with an attack that reduced their health to their starting health times negative one (i.e. negative 30 for a Shotgun Zombie, who starts with 30 health), they would be gibbed. This was a reasonable result when they were hit by rockets, but picking up a special [[strike:"Berzerker"]] "Berserk" power-up enabled the player to [[MegatonPunch gib enemies with his bare hands]].

* NamelessNarrative: 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"

''Doom'' is an [[UltraSuperDeathGoreFestChainsawer3000 ultra-violent]] FirstPersonShooter developed and published by Creator/IdSoftware on December 1993. A follow-up to ''VideoGame/Wolfenstein3D'', ''Doom'' was an astronomical leap forward in video game design, and an even bigger step when it comes to [[{{Gorn}} video game violence]].

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 [[TropeNamer almighty]] {{BFG}}, a massive weapon which could reduce entire rooms of monsters to viscera. Even the player's own face, shown in-between the health and armor counter, became increasingly battered and bloodied with damage like in ''Wolfenstein''.

Another feature was expansion of the weapons. ''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''.

''Doom'' built upon the formula established by ''Wolfenstein 3D'' and expanded upon it, becoming a TropeCodifier 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 [[StandardFPSGuns 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. [[ASpaceMarineIsYou Even the game's basic premise would become a trope]].

''Doom'' was also incredibly [[GameMod 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 score card 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 Creator/JohnRomero, 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'' is one of the most influential -- and infamous -- games of all time.

''Doom'' has been ported to many, many console systems over the years. The UsefulNotes/PlayStation and UsefulNotes/SegaSaturn 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, 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, [[ExaggeratedTrope Babbage's difference engine]] aren't far off the mark at this point. The game also used a creepy and distinctive [[DoomDoors sound effect for doors opening]], which has been re-used in many SpeculativeFiction series for all sorts of things.

''[[VideoGame/DoomII Doom II: Hell on Earth]]'' (1994) sees [[HellOnEarth the demons invading Earth.]] It was also a huge financial and critical success. ''VideoGame/FinalDoom'' was released the same month as ''VideoGame/{{Quake}}''; it was identical to ''Doom II'', but came with two different {{Expansion Pack}}s: ''TNT: Evilution'', created by the third party [[GameMod 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' time, generally considered the hardest of the official packs. ''Final Doom'' was also the game that included a 32-bit UsefulNotes/{{DirectX}} version of the Doom engine, making it possible play ''Doom'' on Windows 95/98 and XP machines, besides virtual machines like UsefulNotes/DOSBox or the many source ports. It received another updated port utilizing the UsefulNotes/{{Unity}} engine 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 has 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.

A decade later, ''VideoGame/{{Doom 3}}'' (2004) was released. Actually the fourth installment, and also a reboot rather than a sequel, it breaks with the first three significantly, with a dark, oppressive tone much more akin to a SurvivalHorror than anything. It was this incarnation on which [[Film/{{Doom}} 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, [[ScrappyMechanic 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.

As for other products in the franchise, there are two cell phone-based {{RPG}}s, an [=iOS=]-based RailShooter, and a board game with expansion pack. For mods and fan games, see FanWorks.{{Doom}}.

* AcidPool: 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 a full protection against them, but only for a limited time.
* AdvancedMovementTechnique: This game and its sequel share a common speedrunning tactic known as straferunning. When you run diagonally, depending on what keys you are holding during, 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.

* AlienBlood: 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 developer 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.

** 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 games' protagonist is deliberately not given a name because it's supposed to be '''''you''''', the player.
* AlwaysChaoticEvil: The demons all have nothing but malicious intent towards everyone and everything around them - even other demons, if one of them [[SetAMookToKillAMook hits another]].

** 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 UnintentionallyUnwinnable due to an unlucky Lost Soul disappearance.
* ArmorMeter: 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.
* ArmorPoints: Doomguy's armor provides a better defense against melee attacks and projectiles when armor points are collected in the levels. There are powerups that can raise its 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.

** In the HarderThanHard "Nightmare!" difficulty, monster projectiles are faster, Pinky demons move faster, and enemies respawn several seconds after death. Oh, [[NoFairCheating and you can't use cheat codes]]. You also recieve the same doubled ammo bonus as in the "[[EasierThanEasy I'm Too Young To Die!]]" difficulty. You'll need it.

** One of the computer screens in the starbase texture set contains the words "Tei Tenga", which was the name of the original 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 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 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 monsters 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).

* ArtisticLicenseMedicine: Somehow Doomguy can use as many stimpacks and medikits as he wants without overdosing on all the stimulants and narcotics that must be in his system.

* ArtisticLicenseSpace: 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 kilometers 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).

** 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 which can teleport a player into another copy of himself, resulting in a recursive TeleFrag ([=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 [[TimedMission 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 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 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 which 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.

* ATeamFiring: 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.

* AutobotsRockOut: The first game and ''VideoGame/DoomII'' both use generic MIDI versions of heavy metal songs for its 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." [[https://doom.fandom.com/wiki/Doom_music This page]] on the ''Doom'' wiki details the various inspirations for the music; for instance, the famous riff from [=E1M1=] was taken from Music/{{Metallica}}'s "No Remorse".

* BlackoutBasement: 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 [[NightVisionGoggles Light Amplification Visor]]. In the worst offenders, it's easier to navigate 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".

* BloodySmile: The Space Marine's mug is in the center of the status bar. As he takes damage, his head gets more disheveled 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.

** 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 that resulted in a stretched image. Later patches fixed the aspect-ratio while keeping the border art up until September 3, 2020 update that implemented official 16:9 widescreen presentation with the option of the original 4:3 display, however, the game's used unused space are filled with the background image of the game's IWAD similarly to the DOS version.

* BossOnlyLevel: 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 Lost Souls to the former and Cacodemons and a Baron of Hell to the latter).

** 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 ([[DegradedBoss 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.

** 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.

** Episode I's ''Military Base''. Coming right after three fairly easy levels even at higher difficulty setting, this is a serious challenge for beginners. 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 center 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 much 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.
* BulletHell: The game (and any of its sequels) can become this if you meet too many enemies at once, in particular on [[HarderThanHard Nightmare!]] difficulty, which speeds up enemy projectiles and causes enemies to respawn on death. Even outside of Nightmare! difficuly, there are enemies that are happy to shoot you on sight, including homing missiles courtesy of [[DemBones the Revenants]], and hitscan enemies whose attacks you can't even dodge.
* BunniesForCuteness: 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 ''[[ItsPersonal before]]''...

* ChainsawGood: The chainsaw replaces your fists as the EmergencyWeapon 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 [[OffscreenStartBonus 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, [[HitboxDissonance 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.

* ColorCodedMultiplayer: The first game's multiplayer has each player a different color. One of the colors is brown, and this mixed with the oldschool graphics and brown colored enemies can cause problems.
* TheColoredCross: The original releases of ''Doom'' and its earlier console ports featured a red cross for the stimpacks, medikits, 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 red-and-white pill. The 2019 Unity ports later replaced the pill icons with a green cross instead.

** A combination of FakeDifficulty 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.

* CoversAlwaysLie: The cover of the first game shows the Marine wielding what seems to be some kind of sub machine 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 ''Videogame/Doom3'', albeit with a redesigned appearance.
* CrateExpectations: About two-fifths of [[http://doom.wikia.com/wiki/E2M2:_Containment_Area_%28Doom%29 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 sourceport Skulltag has a skin which ''is'' a crate.

** The final weapon, the [[{{BFG}} BFG 9000]], deals 3150 average damage (and, due to ''601'' dice rolls being done, very little deviation from that). The [[FinalBoss Spider Mastermind]], in comparison, has 3000 health. This means the final boss of ''Doom'' can be slaughtered in ''one 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).
* CutAndPasteEnvironments: 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. [[RemixedLevel 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.

** 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 was 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.

** The Cyberdemon takes a lot of hits[[note]]About 400 bullets, 45-50 rockets or 150-200 plasma rifle shots. The BFG takes it down in only four blasts, but you don't have access to it during Episode 2 of the first game.[[/note]], 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 "[[CaptainObvious 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 [[SuspiciousVideoGameGenerosity huge]] supply of ammo for your Rocket Launcher, which is (at that point in the game) the weapon with the most raw power. Problem is, 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 [[EnergyWeapon Plasma Rifle]] instead. Thankfully when he appears again [[spoiler: in the secret level of episode 3]], you might've finally found '''[[TropeNamer the]]''' {{BFG}}, which makes the rematch [[CurbStompBattle a lot easier]].

* DarkIsNotEvil: Your SpaceMarine character has some pretty strong BloodKnight qualities (just look at his [[SlasherSmile diabolical grin]] when he picks up a new weapon), and he wound up stationed on Mars due to a violent case of insubordination. His offense, by the way, was putting his C.O. in a body cast for ordering their squad to fire on civilians.

** And then there's what they do to Doomguy's poor little bunny in the ending of the first game, killing it and mounting its head on a spike as they invade Earth.

** The Cyberdemon debuts as the boss of the second episode, then reappears as a BossInMookClothing 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 FinalBoss of both Episodes 3 and 4.

* DescendingCeiling: 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 being a surprise trap covering the key.

* DifficultButAwesome: 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.

* DoorJam: Many traps in the first game and ''VideoGame/DoomII'' locks 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.

** "Hell Beneath", the first level of the new episode from ''The Ultimate Doom'', is known as one of or the hardest level 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 aformentioned 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.

* DudeWheresMyReward: 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 [[spoiler: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".

** The [[SawedOffShotgun Super Shotgun]] isn't in this game, which feels jarring as it would later be treated as one of the Doomguy's {{Iconic Item}}s, his [[ShotgunsAreJustBetter go-to weapon]] for situations that don't quite warrant [[TooAwesomeToUse 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 proper until ''VideoGame/DoomII''.

** The original game was divided into three episodes, with a fourth being added in the UpdatedRerelease ''Ultimate Doom''. The player [[BagOfSpilling 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 [[TheHeroDies is ambushed at the end of the first episode and dies]], waking up in Hell. ''VideoGame/DoomII: 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 DualBoss are two Barons of Hell, which are also the only ones in the episode); and defeating them isn't an InstantWinCondition, 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 Creator/JohnRomero (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 installments like ''VideoGame/Doom3'' and ''VideoGame/{{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.

* EasierThanEasy: While it's not immediately obvious to the player, "Hey, not too rough" (the second difficulty) is the one internally labeled "sk_easy". "I'm too young to die" (internally "sk_baby") uses the exact same thing placements, but [[NumericalHard gives the player double ammo and halves their damage taken]].

* EquipmentBasedProgression: In the classic games, the player gets stronger as they find better and powerful weapons, and finding your first ammo backpack permanently gives you double the ammo capacity.

* EverybodysDeadDave: This sets the stage for the first game, when the hero is the only surviving member of a squad of marines sent to ''two'' survivorless moons (overrun by demons go figure) and then ''Hell.''

* ExcusePlot: Demons have invaded Phobos/Earth! Go kill them all in an over the top and gory fashion.

** 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 UsefulNotes/{{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 [[VeryFalseAdvertising screenshots of simulated gameplay to give the impression of advanced graphics]], while none of the [=WADs=] included remotely matched the screenshots.
* ExpressiveHealthBar: 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 InvincibilityPowerUp, the portrait will display GlowingEyesOfDoom. Receiving damage will cause the character to grit his teeth in pain, or (in certain version of the game) make [[https://doomwiki.org/wiki/Ouch_face a shocked face]].

** 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 LuckBasedMission 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 frustrating problem.

** The Cyberdemon is tall and imposing, with its first appearance in episode 2 showing that [[TheWorfEffect it mutilated four of the episode 1 bosses]] 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 {{Mook}}s. Later games based on the engine (i.e. ''[[VideoGame/FinalDoom Plutonia Experiment]]'', ''VideoGame/Doom64'') usually used level design perks (i.e. small rooms, tight corridor mazes) to prevent you from simply circle-strafing him to death.

* FirstPersonShooter: The ''Doom'' games were known as "Doom clones" for several years before games like ''VideoGame/{{GoldenEye|1997}}'' and ''VideoGame/HalfLife'' did things ''Doom'' didn't and the name "first person shooter" became common.

** At the end of the first episode, you go into a teleporter and are "killed" by a group of monsters.[[note]]The floor is a special type of damaging floor that deals lava damage, even through God mode, and then ends the level once you're brought down to about 10 health; the monsters just make it go faster and feel more intense.[[/note]] Then you find yourself on the lost moon of Deimos, which happens to have been transported into the Hell dimension.
* FiveSecondForeshadowing: Per 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.

* FriendlyFireproof: Both the game and its sequels show a famous aversion. When two demons' attacks collide, they'll prioritize and attack each other instead of [[PlayerCharacter Doomguy]]. Causing monster infighting is actually encouraged on some levels, especilly one in ''VideoGame/DoomII'' with both [[DamageSpongeBoss a Spider Mastermind and Cyberdemon]].

* FromZeroToHero: The backstory of the game is that [[ASpaceMarineIsYou the Marine]] was sent to Mars as a [[ReassignedToAntarctica 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 looksee. 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.

* GainaxEnding: The ending to the first episode is like this intentionally. After you beat the [[DualBoss 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 [[LampshadeHanging lampshades]] how ridiculous this ending is after all you've been through. Most likely, this was meant as a sort of SequelHook 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.

** 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 "[[https://knowyourmeme.com/memes/it-runs-doom It Runs Doom]]" meme, referencing the fact that ''Doom'' has been ported to [[https://www.vice.com/en/article/qkjv9x/a-catalogue-of-all-the-devices-that-can-somehow-run-doom a huge variety of electronic devices, including several that were not designed to run video games in the first place.]]

*** ''Doom 32X Resurrection'' is a project that takes the admirable but disappointing [[UsefulNotes/SegaGenesis 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 makes better use of the Genesis's soundchip.
*** ''[=PlayStation=] Doom: Master Edition'' is a project based on the UsefulNotes/{{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'', ''VideoGame/{{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 in new options and support for [=DualShock=] controllers.
*** The UsefulNotes/GameBoyAdvance ports of ''Doom'' and ''Doom II'' has 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.

* GatlingGood: 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 is more akin to an assault rifle; in ''VideoGame/{{Strife}}'' (another Doom-engine game released a few years later), the weapon is even redrawn into a rifle, and behaves convincingly enough.

** 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 possess[[note]]for example, the aforementioned Revenant rocket is one of the most dangerous attacks any enemy possesses, yet it is a less effective and weaker attack than the Doom Guy's simple Shotgun, and outside the Spider Mastermind and Cyberdemon, enemies that possess a weapon the Doom Guy has have a strictly inferior version[[/note]]. However, the Marine only has 100 HP at base (even less than the aforementioned Pinky), and at max health and armor has the equivalent of 400 HP (which most higher demons exceed).
* GlowingEyesOfDoom: 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!

* {{Gorn}}: One of the games of the 90s, alongside the likes of ''Franchise/MortalKombat'', 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!) [[LudicrousGibs 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.

** 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 indicator ingame 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 have 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 had no armor or a 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 farther 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 the 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 increase the damage of your [[EmergencyWeapon 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 [[InterfaceScrew 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 in a map will still heal you up to 100 and temporarily tint the screen red but will not farther 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 SplashDamage 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.

* HallOfMirrors: ''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 surface in the level geometry that has no texture. It can also happen if more than three warpzones 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.
* HandWave: The manual for the UsefulNotes/AtariJaguar 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.

* HardModeFiller: [=E3M9=] "Warrens", the SecretLevel in Episode 3, starts out as completely identical to the episode's first level. Until you reach the [[YourPrincessIsInAnotherCastle "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. The 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.
* HardModeMook: 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 ''VideoGame/DoomII''-specific enemies [[EarlyBirdCameo to appear in]] ''Doom 1'' levels on higher difficulties, such as [=E1M1=] including a chaingunner and pain elemental on Ultra-Violence.

* HarderThanHard: The aptly-named "Nightmare!" difficulty, the only setting where monsters you've killed will {{respawn|ingEnemies}} several seconds after they die. The monsters also [[MoreDakka 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 [[DeathIsASlapOnTheWrist let the players respawn, too.]]

* HazmatSuit: You can find them in 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.

* HealthyGreenHarmfulRed: Most versions, up to the Collector's Edition, has 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.

* HelpfulMook: Almost any enemy can be helpful since [[SetAMookToKillAMook enemies can damage each other, causing them to infight]]. This is an important tactic on higher difficulty levels.

* HeroTrackingFailure: 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 pro-skills tactic for ''Doom'' -- the default control scheme exclusively used the keyboard and made moving and aiming simultaneously almost impossible.

** Hitscan attacks (bullets, BFG tracers and melee) can completely fail to hit its target depending on where the shooter and the victim are standing in open space, even at point-blank range. This is due to the [[http://www.doom2.net/doom2/research/things.html 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 ''center'' 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 which 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.

* HyperspaceArsenal: 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.

* IdiosyncraticDifficultyLevels: The difficulties are split into three categories of "easy" difficulties, a "medium" one, and "hard" ones, which add more and tougher enemies as you go up. The manual also has explanations for them:
** ''[[EasierThanEasy 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]]Early alpha builds called this one "I Just Want to Kill", and the graphic for it on the menu is still labeled "M_JKILL".[[/note]]

** The 2019 Unity ports added ''Ultra-Violence+'': same as regular Ultra-Violence, but with the turbo enemies from Nightmare as well as things which normally only spawn in co-op modes appearing.

* InstantWinCondition: 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 won 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.

* InvisibilityCloak: 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 playerbase 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 [[TheComputerIsACheatingBastard "accidentally"]] compensate for your movement). The Spectre also has this effect, albeit permanently turned on.

** "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 particular 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.
* KillTheLights: Picking up the blue key in the third map of the first game extinguishes all the lights in the room and opens a MonsterCloset 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 [[RocketJump accessing the third episode's secret level]]. A good shotgun blast or rocket hit was also the only way for non-flying enemies to [[EdgeGravity 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 can 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 insistance, the [[ChainsawGood chainsaw]] delivers no knockback to insure it has the intended effect of ripping into targets rather than pushing them away.

* LadderPhysics: 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 ladders that you can somehow drown on or the Doomguy having SuperNotDrowningSkills.

* LethalJokeWeapon: If you pick up a Berserk Pack, then your fists become this. After picking up said powerup, 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 that 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).

* LevelInReverse: The secret level for the 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.

* LightningBruiser: 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.

* LockAndKeyPuzzle: 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-color 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 [[GameMod custom WADs]], a man-made electronic keycard doesn't open.

* MalevolentArchitecture: The original batch of games say 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 BenevolentArchitecture.

* 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 [[EvilIsNotAToy screwing around]] by using Hell as a pseudo-wormhole in order to teleport things between their Phobos and Deimos bases. This, predictably, [[GoneHorriblyWrong 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 BigBad).

** 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 monsters unteleported, simply sitting there; in those instances, noclipping inside the rooms is the only way to get 100% kills.

** 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 invulsphere that you can't reach and a door that's too thin for the secret to register. These can be triggered by noclipping, however.

** There are also several instances where 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.

* NighInvulnerability: Due to how it's programmed, the [[GodMode 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's only two things in the unmodified games that can kill him in that state: {{telefrag}}s, 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).

** Generally averted for the base, vanilla game. ''Doom'' was made at a time when a large percentage of gamers would play with keyboard only, no mouse, and the default difficulty level, Hurt Me Plenty, seems balanced with that in mind. Many veteran ''Doom'' players recommend even a first playthrough should be on Ultra-Violence for a difficulty curve more fitting for modern FirstPersonShooter players.

** When playing the whole game with fast monsters or on the Unity ports' UV+ difficulty, Ultimate Doom and Doom II can get very difficult, the latter of which enables fast monsters and multi-player only spawns. On Nightmare difficulty, the game becomes outright HarderThanHard, with only a small fraction of players being able to beat the entire games on Nightmare.

* NothingExcitingEverHappensHere: The basis for the original game, being the marine's [[ReassignedToAntarctica 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.

* {{Novelization}}: Four books based off ''Doom'' and ''Doom II'' (with the first two being actual novelisations of the game's storyline, such as it was). And two more based off ''Doom 3''.
* NuclearCandle: The actual effect of the [[NightVisionGoggles Light Amplification Visor]] is to brighten the whole map to max level.

* OneHitPolykill: 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 shotgun's multiple pellets.

* OnlyAFleshWound: Being a health-bar-based shooter, the game does this with tougher enemies and averts with weaker ones, which can be [[LudicrousGibs 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.

* Over100PercentCompletion: The game can tabulate a kill percentage above 100% on any level with an archvile in it, since archviles can resurrect dead monsters, except other archviles. A player routinely has to down the same enemy multiple times before concentrating fire upon the archvile 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.
* OverdrawnAtTheBloodBank: ''Doom'' was one of the few video games in the early '90s that demonstrates that 2D sprites can spill lots of blood shot and killed, and some enemies can be gibbed when killed by high-powered weapons.

* PlotCoupon: The Blue, Yellow, and Red keys, when playing in single player mode.

* PowerUpLetDown: 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.

* RandomNumberGod: Nearly every attack in the game, from both the player's weapons and demons' attacks, deal randomized damage, with the only exceptions being SplashDamage (where the amount of damage is determined by how close you or the monsters are to the center of the splash damage source) and the launching hit of the Archvile'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 Archvile'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. [[https://www.youtube.com/watch?v=pq3x1Jy8pYM This video]] explains how the random number generator works, while [[https://www.youtube.com/watch?v=1fcqYr1NevE this video]] delves farther into enemy stats and shows the aspects that are randomized, while [[https://www.youtube.com/watch?v=GLeMj-OYV1c this video]] does the same for the players' weapons.

* RealIsBrown: The original game was noted for its "realistic" graphics, back in its day. Sure, plenty of levels go for muddy browns and grays, 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.

* RoadRunnerPC: 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).

* RocketJump: UrExample 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 rocketjump... though it can be reached just by straferunning.
* RocketTagGameplay: Given the HealthDamageAsymmetry, death matches between players is 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).

** 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 texture cheats to create the illusion of sloped or curved arches are incredible.

* SecondPersonNarration: The narrations at the end of each episode are in second person.

** Each Episode in ''Ultimate Doom'' has a secret map that are accessible via a secret exit in one of the Episode's maps:

*** 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''', being 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, [[VictoryFakeout 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 precededing 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 nor any of the other ports:

*** 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, [[spoiler:loud rave music starts playing as the player enters a strobelit 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 one 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 it 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.
* SensoryAbuse: An infamous genre of WAD, referred to as Terry [=WADs=] after the troll who made the first examples, are 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 [[BlackComedyRape anally raping the reader]].

*** The first area of [=E3M1=] didn't have enough ammunition to kill all the {{Beef Gate}}s. It was 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 fighting each other, then maneuver 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 [[DopeSlap bite it back in retaliation]] and appearing to argue with each other before one eventually misses and they both resume their attack on the player.

** One of the most well-known examples, ''Doom'' is probably the one title above all others which 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 in the main pages of British ''PC Format'' magazine, instead of being relegated to the shareware section.
** Carmack has [[http://www.wired.com/gamelife/2013/12/john-carmack-doom/ said in a 20th-anniversary interview]] that shareware was actually not such a great fit for ''Doom''. Not because 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 need of any marketing gimmicks.

* ShootTheMedicFirst: In [[GameMod ZDoom]], it is possible to create enemies that can resurrect fallen foes via Decorate. Death for these guys should be top priority.

** The original pump-action shotgun has a modest spread which 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 SniperRifle.

* SinisterNudity: 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 archviles traipse about naked.
* SkeletonKey: 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.

* SplashDamageAbuse: 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 which is close to an explosion but very far beneath or above it will still take damage. [[https://www.youtube.com/watch?v=ERzwBQFLQXY Demonstrated in this video.]]

* StoneWall: The Baron Of Hell isn't much 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 resiliant 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 Archvile, or to act as "doors with health" that block players from accessing areas without expending an unhealthy amount of ammo and time.
* StrangeSecretEntrance: Some of 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.
* StupidEvil: The demons will ignore their primary target of the Doomguy to attack their allies if they were accidentally hit in the back.
* SummonBiggerFish: 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 fool enough to draw their attention.

* SurrealHorror: One thing that stays consistent [[ContinuityReboot throughout the franchise]] is that Hell is ''really [[{{Pun}} Goddamn]] [[EldritchLocation weird.]]'' The laws of physics as seen in our reality [[RealityIsOutToLunch 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 being made of spinal columns and human faces.

** [=E2M8=] givesyou 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).

* TeleFrag: 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 splats them. To be exact, "invulnerable" (whether by PowerUp or by GodMode cheat) means "immune to attacks scoring 1000 {{Hit Point}}s or less of damage". A telefrag is the only source of damage to surpass that, doing 10,000 HP damage.

* TeleportSpam: It is possible to make an invisible teleporter which works only for monsters.

* ThereIsNoKillLikeOverkill: 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 sastifying death animation of them [[LudicrousGibs exploding apart]], referred to as gibbing. Doom Guy himself can also be gibbed by especially powerful attacks.
* ThisIsGonnaSuck: The hardest difficulty setting is Nightmare!, featuring faster monsters that respawn shortly after being killed, and most cheat codes 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? [[HarderThanHard This skill level]] [[TheComputerIsACheatingBastard isn't even remotely fair]]."
* ThisLooksLikeAJobForAquaman: Normally the Partial Invisibility powerup is a [[PowerupLetdown 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 [[LuckBasedMission 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 amount of hitscanners, especially Chaingunners, Partial Invisibility becomes immensely useful. [[note]]Clever use of Partial Invisibility is practically required to complete some levels on the ''Nightmare'' difficulty (e.g. Map 8 of ''TNT: Evilution'') due to the enemies' relentless and berserk nature, and many fan-made maps will require usage of invisibility to survive a hitscan ambush.[[/note]]

* ToxicInc: Never mind the demons from Hell, the UAC cannot be doing anything good for the Martian enviroment with all the deadly radioactive waste they have lying around. As the DOOM Guy himself notes in the ''ComicBook/{{Doom}}'' comic:

** For the FPS genre. Until about 1998, where the genre [[VideoGame3DLeap shifted to full 3D]] with games like ''VideoGame/GoldenEye1997'' and ''VideoGame/HalfLife1'', they weren't even called "first-person shooters", but were instead "''Doom'' clones".

* UnendingEndCard: 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 case of the former, the game's manual incorrectly states the player will be cycled back to level 1.

* UniqueEnemy: The Playstation port of the original game features a single translucent Cacodemon that's locked in a cage in the level Tenements. [[SubvertedTrope 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.
* UntitledTitle: The levels "Fortress of Mystery" ([=E2M9=]) and "Hell Keep" ([=E3M1=]) has the music track "Untitled", possibly because "MIDI Version of [[Music/{{Pantera}} Mouth for War]]" was too cumbersome and opened the door for litigation.
* UnwinnableByDesign: 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 [[HopelessBossFight the hero is SUPPOSED to die]], and in fact [[FissionMailed that's the only way to complete the episode]].

** The 2019 ''DOOM Enhanced'' editions of ''Doom I'' and ''II'' for [=PlayStation=] 4, Xbox One, Nintendo Switch, and mobile devices, after multiple patches, features 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 ''VideoGame/{{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, 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=].

* VisibleInvisibility: A weird example: The invisibility sphere (more accurately named "partial invisibility" in game) turns you into a sort of staticy looking 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.

* WrapAround: The mapspace 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 mapspace, notably with monster pathfinding not considering the open border of the mapspace to be a valid pathway.

* DownloadableContent: 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, ''{{VideoGame/{{Sigil}}'' for ''Doom'', and ''No Rest for the Living'' for ''Doom II'' with other mods added through content updates.

** 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 UnwinnableByMistake due to an unlucky Lost Soul disappearance.

* DeadGuyOnDisplay: 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 [[ImAHumanitarian snacks for later]].

* DownerEnding: The marine in the first ''Doom'' succeeds in escaping Phobos, climbing down from Deimos and escaping Hell itself, only to find that the demon invasion has already taken hold on Earth, with billions being slaughtered. TheEnd! ''The Ultimate Doom''[='=]s fourth episode and the sequel have you saving what's left of humanity and [[EarnYourHappyEnding 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.

** The [[SawedOffShotgun Super Shotgun]] isn't in this game, which feels jarring as it would later be treated as one of the Doomguy's {{Iconic Item}}s, his [[ShotgunsAreJustBetter go-to weapon]] for situations that don't quite warrant [[TooAwesomeToUse the BFG-9000]]. Some fans who haven't played the original ''Doom'' don't realize that this weapon isn't in this game.

* KickTheDog: The demons kill a bunny and put its 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.

* KickTheDog: The demons kill a bunny and mount its 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.

The ''[[TropeCodifier archetypal]]'' FirstPersonShooter.

'''''{{T|ropeCodifier}}he''''' [[UltraSuperDeathGoreFestChainsawer3000 Violent Video Game]].

''Doom'', Creator/IdSoftware's December 1993 follow-up to ''VideoGame/Wolfenstein3D'', was an astronomical leap forward in video game design, [[{{Gorn}} and an even bigger step when it comes to video game violence]].

** With the development of circle-strafing and mouse-aiming, even the mighty Cyberdemon has become this, at least in the original game. Later games based on the engine (i.e. ''[[VideoGame/FinalDoom Plutonia Experiment]]'', ''VideoGame/Doom64'') usually used level design perks (i.e. small rooms, tight corridor mazes) to prevent you from simply circle-strafing him to death.

** Controlling the original game with just the keyboard or 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.

* BrutalBonusLevel: Episode II's secret level, ''Fortress Of Mystery''. You begin the game in the center 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 much 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.
** To a lesser extent, Episode I's ''Military Base''. Coming right after three fairly easy levels even at higher difficulty setting, this is a serious challenge for beginners. 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.

The '''''[[TropeCodifier archetypal]]''''' FirstPersonShooter.

'''''The''''' Violent Video Game.

* HopelessBossFight: Episode 1 of the original game ends this way. Right after defeating the DUalBoss 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.

* BorderOccupyingDecorations: 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.

* GatlingGood: The Chaingun. It's been a series staple and can [[MoreDakka mow down most enemies in seconds]]. The only time it becomes ineffective is against bosses. Despite its threatening appearance, though, its fire rate and behavior is more akin to an assault rifle; in ''VideoGame/{{Strife}}'' (another Doom-engine game released a few years later), the weapon is even redrawn into a rifle, and behaves convincingly enough.

** The Marine himself is one; he moves incredibly 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 possess (for example, the aforementioned Revenant rocket is one of the most dangerous attacks any enemy possesses, yet it is a less effective and weaker attack than the Doom Guy's simple Shotgun, and outside the Spider Mastermind and Cyberdemon, enemies that possess a weapon the Doom Guy has have a strictly inferior version). However, the Marine only has 100 HP at base (even less than the aforementioned Pinky), and at max health and armor has the equivalent of 400 HP (which most higher demons exceed).

* GoldenSuperMode: The Space Marine's eyes become golden when the god-mode cheat is entered.

* DeliberatelyMonochrome: The invincibility powerup turns everything black and white while active, most likely so it's obvious when it wears off.

* AcidPool: Starting from [=E1M2=], 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 a full protection against them, but only for a limited time.

* BareYourMidriff: A rare male example. The marine on the cover art has his belly exposed. This seems to be a very strange armour design choice, but looking closely at the actual art (the in-game digitization is a bit harder to make out) shows the chest hole was torn open (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).

* ClothingDamage: 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 [[BareYourMidriff with an abdominal cutout]].