Doom 3 (Remake)/References

Doom and Doom II

 * The entirety of the original Doom and Doom II: Hell on Earth are unlockable as side-games via inputting the passwords "ULTRAVIOLENCE" and "MISSUDAISY" as the opening passwords to the computer in Sergeant Kelly's bunker. The games themselves are modified significantly from the original.
 * There are eleven new weapons, bringing the number of weapons available to the player up to twenty. In addition to this, the Super Shotgun from the second game is now available in the first game. There is a option to exclusively use the original loadout alongside four of the newly introduced weapons, known as "Boomer".
 * The Axe, based upon the weapon from Doom RPG and used as both an alternate melee weapon that can kill the lightest enemies in a single hit or break down certain doors. It is equipped under weapon slot 1 with the Fists.
 * The Auto Pistol, functioning like a faster version of the HacX pistol and resembling the unused gun seen on the original cover art. It is equipped under weapon slot 2 with the Pistol.
 * The Machine Gun, based on the scrapped concept from the original game and functioning similar to the machine gun in the main game. It is equipped under weapon slot 4 with the Chaingun.
 * The Grenade Launcher, based on the weapon from Strife that functions as a less-powerful, gravity-bound Rocket Launcher with a larger blast radius and a faster firing rate. It is equipped under weapon slot 5 with the Rocket Launcher.
 * The Flamethrower, based on the weapon from Strife and the SNES port of Wolfenstein 3D that functions as a close-range weapon that can swiftly kill most enemies and can leave behind physical fires to form temporary traps for enemies, but consumes ammunition at a rapid rate. It is equipped under weapon slot 6 with the Plasma Gun.
 * The Unmaker, a scrapped weapon from the game's planning stages that was later included in Doom 64 that functions akin to a railgun and does not possess ammo pickups, instead gaining shots by killing enemies. It is equipped under weapon slot 7 with the BFG 9000.
 * The Hand Grenades, which function similar to the grenades in the main game. They are equipped under weapon slot 8.
 * The Landmine, based upon the Kinetic Mine from DOOM and serving as a highly powerful trap for luring out demons, detonating when a enemy steps onto it and doing enough damage to kill most enemies lighter than a Baron of Hell. It is equipped under weapon slot 8 with the Hand Grenades.
 * The Probejectile, based on the scrapped concept from the original game (and utilizing a modified sprite from the beta's machine gun) which functions as a minimal damage, remote-controlled projectile that can attach to an enemy and identify their weaknesses, temporarily disable an invisible enemy's concealment, or do heavy damage to a cybernetic enemy. It is equipped under weapon slot 9.
 * The Fire Extinguisher, based on the Doom RPG weapon that is used to extinguish fires to allow access to certain secret areas as well as damage certain enemies such as the Lost Soul and Pain Elemental. It is equipped under weapon slot 9 with the Probejectile.
 * The Dark Claw, another scrapped concept from the beta of the original that functions as a continuous beam of mid-range highly damaging energy with no individual ammunition, instead slowly draining the player's own health to power it. It is equipped under weapon slot 0 with the Chainsaw.
 * The original weapons are changed somewhat to accommodate the new playstyle. All also have new additional sprites to allow them to have smoother animation.
 * The Fist's damage and range are slightly increased. Its alternate fire is a uppercut that does more damage, but swings slower.
 * The Chainsaw is equipped under weapon slot 0 rather than weapon slot 1, and makes different sounds. Its alternate fire is a sideways swipe that functions like a axe attack but with more damage. The message when acquiring it is changed from "A Chainsaw! Find some meat!" to "A Chainsaw! The great communicator!".
 * The Pistol now has a pickup sprite, does more damage, fires slightly faster, and is more accurate. Its alternate fire is a
 * The Shotgun does less damage, but fires and "reloads" faster. Its ammunition is now referred to as Shotgun Shells. Its alternate fire is to throw a flash grenade that does no damage to enemies but temporarily stuns them, although it does not work on certain enemies such as the Arch-Vile.
 * The Super Shotgun is slightly more accurate, but is otherwise unchanged. Its alternate fire is to fire one barrel after the other, with each doing the same damage as a point-blank Shotgun blast.
 * The Chaingun does slightly more damage per shot and no longer shares ammunition with the Pistol, instead using its own ammunition type in the form of Chaingun Shells. Its alternate fire is to spin up the barrel silently without firing.
 * The Rocket Launcher does more damage and has a faster projectile speed, but has a smaller blast radius and does less splash damage. Rocket jumping is also more heavily used, with the player taking much less splash damage from rocket jumping and new paths being available.
 * The Plasma Gun does slightly more damage and has a slightly faster projectile speed, but fires slightly slower. Its alternate fire is to charge up and then release a heavy blast of plasma in a similar manner to the Shotgun, costing 25 Plasma Cells.
 * The BFG 9000 has its own unique ammunition in the form of BFG Molecules, but is otherwise unchanged. Its alternate fire is to fire smaller red plasma balls at a faster rate that costs 3 BFG Molecules per shot, based upon the scrapped beta concept for the BFG.
 * In addition to the new weapons, there are also new variants of enemies, and each also now has at least two different variants. All of the monsters from the original games have been changed somewhat.
 * All enemies are divided into twenty different categories:
 * Slave: Stoned Corpse, Frozen Corpse, Hellslave
 * Zombie: Former Human, Former Sergeant, Former Scientist, Former Recon
 * Trooper: Former Commando,
 * Imp: Imp Troop, Imp Shader
 * Demon: Pinky, Spectre
 * Soul: Lost Soul, Forgotten One, Tortured
 * Cacodemon: Red Caco, Blue Caco
 * Hell Soldier:
 * Hell Noble: Baron of Hell, Hell Knight
 * Reanimated: Revenant, Ghoul
 * Behemoth: Mancubus, Druj
 * Spiderdemon: Arachnotron
 * Spawner: Pain Elemental, Beholder, Blob
 * Hell Priest: Arch-Vile, Apollyon, Infernis
 * Hell Cattle: Hellhound
 * Other: Wolfenstein SS
 * The difficulty levels are changed, and some new skill levels are added. All difficulties also have their own humorous descriptions when clicked on.
 * "I Wanna Play, Daddy!": "For younger players, gamers unfamiliar with first-person shooters, and video game journalists." The player takes 25% of the base damage, starts equipped with the Fists, Axe, Pistol, Auto Pistol, Shotgun and Machine Gun, and begins each level with full health and Blue armour. Enemies take 200% of the base damage and come in half their base numbers.
 * "I'm Too Young To Die!": "You're not invested in the challenge. You just want to kill demons, and that's not a crime." The player takes 50% of the base damage, starts equipped with the Fists, Pistol, Shotgun and Machine Gun, and begins each level with full health and Green armour. Enemies take 150% of the base damage and come in three-quarters of their base numbers.
 * "Hey, Not Too Rough!": "Easy does it! You want to blast demons without having to worry TOO much." The player takes 75% of the base damage, starts equipped with the Fists and Pistol, begins each level with full health, and armour carries over between levels. Enemies take 125% of the base damage and come in their base numbers.
 * "Bring It On!": "The standard Doom experience. Hold off the demon invasion and have fun doing so!" The player takes 100% of the base damage, starts equipped with the Fists and Pistol, and health and armour carries over between levels. Enemies take 100% of the base damage and come in their base numbers.
 * "Hurt Me Plenty!": "If you're not a Doom expert, you will be by the time you complete this difficulty." The player takes 125% of the base damage, starts equipped with the Fists and Pistol, and health and armour carries over between levels. Enemies take 80% of the base damage and come in their base numbers.
 * "I Own Doom!": "You talk the talk, but can you walk the walk? Anyone who completes this difficulty gets our respect." The player takes 150% of the base damage, starts equipped with only the Fists, and health and armour carries over between levels. Enemies take 60% of the base damage and come in double their base numbers.
 * "Watch Me Die!": "An absolutely unfair difficulty reserved for the baddest of the bad. Good luck ... you're gonna need it." The player takes 200% of the base damage, starts equipped with only the Fists, and begins each level with 50% health and armour. Any health gained above 100% will gradually drain until it returns to 100%. Enemies take 40% of the base damage and come in triple their base numbers.
 * If played on the two hardest difficulties or with the "Survival Horror" setting turned on, the games will be darker and use the PlayStation Final Doom soundtrack.
 * Each episode of the first game continues immediately after the other, similar to Doom II, rather than requiring each to be selected from the main menu.
 * The maximum amount of health and armour is increased from 200% to 300%.
 * The standard green Armour absorbs 50% of all incoming damage rather than 33%, and the blue Megaarmour absorbs 75% of all incoming damage rather than 50%. Having any armour also reduces the amount of incoming damage the player takes by 20% with the green Armour and 40% with the blue Megaarmour.
 * The amount of ammunition the player can carry is increased by roughly 50% for all ammunition types. All these numbers are doubled after finding a Backpack, and can be increased further to 999 for each ammunition type after finding enough Backpacks.
 * The Backpack is redesigned to resemble the backpack in the main game, which is in turn a updated retooling of the original design.
 * The secret level introduced in the Xbox port of the first game, Sewers, or "E1M10", is available.
 * The additional level introduced in the Xbox port of the second game, Betray, or "MAP33", is available.
 * There is an additional level added in the first game, known as Memorial, or "E1M0", which is a hall in which the player lacks any weapons and is instead allowed to walk down the hall, which is filled with tributes to multiple members of the Doom community who have since passed away.
 * In addition to this, several official expansions to the games, as well as a handful of fan-made "megawads" that have the "Cacowards", can be unlocked as side-games by completing certain objectives
 * The two megawads that comprised the Final Doom port, TNT: Evilution and The Plutonia Experiment, can also be unlocked as side-games by completing Doom and Doom II on any difficulty. Completing both unlocks the intended third instalment in the series, Perdition's Gate.
 * The official add-on for the original Doom 3: BFG Edition, No Rest for the Living, can be unlocked as a side-game by completing the main game on any difficulty.
 * The official add-on Double Impact by Matt Cibulas and Ralph Vickers can be unlocked as a side-game by completing the main game on Nightmare+ difficulty.
 * Erik Alm's 2003 megawad Scythe can be unlocked by
 * The 2004 total conversion Action Doom, which was famous for its online advertising campaign, can be unlocked by
 * John Romero's unofficial fifth episode for the original game, SIGIL, can be unlocked as a side-game by completing Secret Level 33.
 * The Super Turbo Turkey Puncher 3 game, which uses the fist sprites from the game, is retained.
 * The famous IDDQD (god-mode) and IDKFA (all-weapons) cheat codes can be entered in-game. Doing so will instantly kill the player with the message on-screen of "Trying to cheat, eh? Well, now you die!", award the player the "Nice Try!" hidden achievement and send them back to their last checkpoint save.
 * Secret Level 33, the final secret level of the game, is a recreation of the legendary first level of the first game, Hangar, also known as E1M1.
 * The "Nightmare" difficulty was originally the hardest difficulty of the games, but is instead the second-easiest difficulty of the main game.

Doom 64

 * The main uniform armour worn by the Marines resembles the armour worn by the protagonist of 64 with some elements from the armour worn in the original Doom 3.

DOOM Eternal

 * Eternal noticeably ties into the game's storyline, with
 * A advertisement for the game pokes fun at Eternal with its tagline "No magic swords. No useless arm blades. No ugly, overcomplicated, edgy Tolkien wannabe stories. No backstabbing AIs, and no puke-green heavy metal Warhammer 40k rejects. Welcome to the real word, bitch." The humour of this is ironic, as all these events appear in-game.

References to Other Doom Fanworks

 * The famous Hissy plush Cacodemon, made by Jonas Feragen, appears in Sergeant Kelly's personal quarters on his bed.
 * The infamous "so bad it's good" fanfiction Doom: Repercussions of Evil is referenced by the Imps writing on the walls in blood "JOHN IS A ZOMBIE", "YOU WILL BE KILL BY DEMONS" and "YOU ARE THE DEMONS".

References to Other Games

 * The secret levels of the game, with the exception of the second, fifth, tenth, twenty-fifth, thirty-first, thirty-second and thirty-third, are all recreations of levels in past first-person shooter games.
 * Secret Level 1 is a recreation of Floor 1 of Doom 's predecessor, Wolfenstein 3D. Its placement is a reference to both the placement of the stage in the game and it originally being the first secret map in Doom II. In the German release of the game, all the Nazi imagery is removed.
 * Secret Level 3
 * Secret Level 4
 * Secret Level 6
 * Secret Level 7
 * Secret Level 8
 * Secret Level 9 is a heavily modified recreation of the Team Fortress Classic version of the Team Fortress series' iconic map, 2Fort. Its placement is also a reference to the main number of classes in the games.
 * Secret Level 11
 * Secret Level 12
 * Secret Level 13
 * Secret Level 14 is a recreation of the seventh level of the fourth episode of Quake, Azure Agony. Its placement is also a reference to the original size of the file, 1.4 MB.
 * Secret Level 15
 * Secret Level 16
 * Secret Level 17
 * Secret Level 18
 * Secret Level 19
 * Secret Level 20
 * Secret Level 21
 * Secret Level 22
 * Secret Level 23
 * Secret Level 24
 * Secret Level 26
 * Secret Level 27
 * Secret Level 28
 * Secret Level 29
 * Secret Level 30 is a recreation of Spaceport from Duke Nukem 3D 's second episode. Its placement also references the game's subtitle, with the number 30 standing in for the word 3D.
 * The famous Dopefish from id Software's Commander Keen series appears on the front cover of a book on the desk in Sergeant Kelly's personal quarters.
 * The Neural Stunner, Vorticon Hyperpistol, Flower Power and Boogus Bomb from the Commander Keen series are available as skins for the Pistol, Revolver, HE Grenades and EMP Grenades.