This is an attempt at explaining MetaDoom stuff, such as mechanics, easter eggs, source of resources and stuff etc.
Don't expected 100% accuracy or anything.

==RANDOM SHIT==
* Mod's logo shows off Doom 1, 2, 3 (BFG lost edition image) and 4
* Background represents first levels or early areas of 1, 2, 64, 3, DRPG, D2RPG and 4
* Main theme is a remix based off D4, intermission theme is a E2M3 remaster from Andrew Hulshult and game over theme from ultra nightmare mode is a piano cover of E1M8
* Texts in the TITLEPIC, Quit messages and even game over texts are lines related to/from Doom games, manuals, characters dialouges, lore related shit and even stuff like Repercussions of Evil and a Chex Quest reference (Martian Buddy and SnapMap are referenced, for example)
* Difficulty setting menu uses Doomguy's face in a "Wolfenstein 3D-esque" fashion
* Doomguy has voice sounds related to beta Doom 3
* Generally, a lot of thing may have beta Doom 3 sounds, but also assets from games that aren't even id related
* If gibbed, his face literally explodes, using an animation from PSX Doom
* Female gender option replaces Doomguy with Kira Morgan from D2RPG/Other gender options replaces him with Dr Peters from Doom VFR
* There's optional content like breakable props, secret enemies and some other shit
* Dead marine corpses can have randomized variants based off D64, 3, RPG, 4 and even some cut Doom sprites
* Some gib sprites may come from DRPG
* Sound of doors/crushers crushing bodies may come from Duke Nukem 3D
* Mod normally has a progress based randomization system, but Content Locust makes everything actually randomized
* You also have options for performance based stuff like preventing some monsters from jumping or vanishing blood effects
* Wolfenstein SS have variants staring SNES port soldier, Mac port Officer, Apple stealth Wolfenstein game enemy and Wolfenstein RPG green soldier with RTCW sounds
* Commander Keen has Dangeround Dave, Rescue Rover, Shadow Knights ninja, Catabombs 3D skeleton and a Hovertank 3D citizen
* Keycards have randomized skins based off D64, 3, D2RPG and 4, along with a D4 sound (That one where you take a chip from the dead red armored marines)
* Skullkeys get randomized skins from D64 and D4, along with a D4 sound
* With default keybind being N, there's a codex inspired by 2016, in which info gets filled up with picked up items/guns and killed enemies
* Codex info references ingame lore, text from game manuals, Doom media like the movies (RRTS) and novels (Robotic lost soul, sphere coating someone with a liquid) and even Impse
* Intermission screen plays a sound from D4 everytime you beat a level and it has a score number tracker
* The score system and 6 treasure items (That spawn next to health/armor bonuses) is based off a cut Doom feature, inspired by Wolf 3D
* Besides the 6 treasure items, other score pick ups include a UAC Credit from DRPG and D4 Marineguys based off four different Doom armor designs throughout the series
* Score can also be affected with secrets and kills
* Mod's menu has some hellish runes in the background, possibly Doom 3 related
* ZDoom marines are acknowledged in this mod, so rail gun AI doomguys are implied to have the Gauss Cannon and Berserker guys do the D3 scream noises
* Theres cheat codes too, one of them makes rooms darker to reference D3 (IMPULSE 2004 in console), while another turns floor/ceiling textures into flat colors to reference SNES Doom (IMPULSE 16)
* Kinsie worked on a thing called Consolation Prize where you can play mods in maps from PSX Doom and Doom 64. This led to a special feature in MetaDoom, where Doom 64 items can get "specific" spawn spots for the sake of faithfullness
* If you IDKFA, you get all codex entries and can spawn D64's demonkeys from the inventory
* If your health is low enough, you get a beeping sound from D4
* If you die, Doomguy's hands have a first person animation based off D4
* Throughout updates, versions of the mod had names referencing Doom related characters like some from the novel and D4
* Water splash effects may be Heretic related
* In the player setup, the player's class is "Slayer"
* Intermission screen has sounds like rocket explosion (kills), Wolf 3D treasure pick up (items) and GZDoom secret notifier (secrets)
* Some Doom 2 monsters have "fixed" sprites, probably to fix stuff like Arachnotron's "holes" and a grey thing next to a frame of a Revenant punching
* The "hehee" sound shows up when you do the Impulse cheats

==WEAPONS==
MetaDoom has a lot of toys to play with. Some of them have designs meant to mix up different designs and elements of certain weapons. Some also have alt fires as a nod to D4 and to make things more interesting. There's also some randomization rules where for you to pick up X, you must get Y first except for the melee weapons for some reason.
>FIST
Has its own keybind as is a simple move that makes enemies drop health pick ups when punched, as in D4 fashion
>1st slot: EGM SIDEARM
* Pistol whose design sort of resembles D3 and 4
* Has infinite ammo and shoots laser instead of bullets
* Alt fire is a lantern, which could resemble D3 BFG edition but it's actually based off D3's duct tape mod
* Menu option turns off intinite ammo, so it uses bullets as ammo, obviously
>2nd slot: COMBAT SHOTGUN
* D64 look but still has a normal reloading animation
* Alt fire is D4's grenade shot, costing 4 shells
>2nd slot: HOLY WATER PISTOL
* From D2RPG
* Main fire deals low damage but makes most fows cry and run like cowards, while instantly killing LS's (Origianlly, it just stunned them and dealt more damage on LS's and maybe Archies too but less on zombies, but i might be wrong)
* Second alt fire refills your health but wasters more water
* To refill its ammo, just stand on most liquid textured floors (Originally it was filled with water tanks and using toilets i think)
* When you refill with water, you may heard a sound that is RPG related
>3rd slot: SUPER SHOTGUN
* Has D2's design but with different sprites, animations etc and both fires are the same
* Can show up in Doom 1 sometimes, by replacing Shotty placement
>3rd slot: FIRE EXTINGUISHER
* Doom RPG weapon that can put up Lost Souls, fireball projectiles and even flames/fires from certain props
* Second fire can save you from Archvile's fire attack (I think originally it was mainly used to put up fires blocking paths and deal more damage on LS's and Archies)
>4th slot: ASSAULT RIFLE
* Doom 3's machine gun, which sort of resembles classic Doom's chaingun, but apparently it fires one tick faster, due to complaints of it sounding weak
* Alt fire is D4's micromissiles, which wastes a lot of ammo
>4th slot: CHAINGUN
* Design mostly represents D64 and 3, but painted blue
* Primary fire is obvious, more damage at the cost of waiting times (I thnk it also uses a beta D3 sound)
* Second fire: D4's turret more, unleashing three barrels to do more damage at the cost of ammo (It also prevents you from walking instead of just walking slowly)
>5th slot: ROCKET LAUNCHER
* Design represents D1, 64 and 3
* Firing sound may be D3 related
* Alt fire is from D4, detonating rockets in mid air
>5th slot: GRENADE LAUNCHER
* A weapon from D4's multiplayer DLC
* Like a traditional GL, its grenades either bounce around and explode shortly after or explode on impact with enemies
* Second fire is a gas grenade, that drops short lasting gas, that continues to hurt enemies (Or sometimes you)
* Grenade sprites may be Duke Nukem related, while the green cloud is probably from Hexen
>6th slot: PLASMA RIFLE
* Design and sounds represent classic Plasma gun and D3/4 (Could resemble all versions, actually)
* Has no recoil
* The screen on the weapon shows bars being filled when firing, this is so when they're full, you can use the alt fire
* Alt fire is D4's heat wave, which seems to be composed of stronger Plasma balls than a simple Plasma wave
>6th slot: LIGHTNING GUN
* D4 multiplayer weapon, whose primary fire is a string of electricity that shocks enemies and wastes a bit more ammo
* Alt fire is borrowed from the Plasma gun in D4, which is a harmless projectile that stuns enemies
>6th slot: Gauss Cannon
* D4 weapon, that is pretty much a Quake Rail Gun, kinda
* Design sort of represents the original BFG9000 or at least early sprites and the toy they used for it
* Primary fire even has that spiral effect from Q2 and Skulltag
* Second fire is just a scope for the sake of balance and maybe a page taken from the Vortex Rifle
* If you're too close, it can cause splash damage and hurt you
>7th slot: BIG FUCKING GUN 9000
* Design represents D64 and 4
* Uses seperate ammo from Plasma gun (Argent core)
* Main fire may deal a bit more damage than usual and the projectile can damage enemies nearby, as inspired by D3/4
* Second fire is a stream of BFG balls based off an unused BFG fire (It can even bounce on floors/ceilings) but there's no red projectiles
>7th slot: UNMAKER
* Doom 64's hellish weapon whose design also represents the Reaper (D4 multiplayer DLC) and because it's originally names, it's technically nicknamed after a Doom bible weapon
* Like the original, it starts off as an odd cousin of the Plasma rifle, but once you pick up the demonkeys, it fires faster and gets to shoot three projectiles at once
* Said demonkeys can spawn next to BFG/Unmaker spots and in D64 maps (Consolation Prizes), they're where they're supposed to be
* Demonkeys also unlock and upgrade an alt fire, where you charge up 1 to 3 laser beams
>7th slot: SOULCUBE
* Doom 3's magic cube whose design is based off Doom 2's spawn cube
* Once picked up, enemies start dropping "soul essance" and you need at least 10 of those to make the weapon work (May be based off D4's MP mode called Soul Harvest)
* Once you got 10 souls, you can use the Cube to instantly kill one enemy and they'll drop ammo/health/armor like in D4 fashion
* Despite being a BFG replacement, it can replace chainsaw in rare occasions (E2M5, Map 10)
>8th slot: Chainsaw
* It's design and sounds mostly resemble later designs but it's technically just a yellow chainsaw, so it may not matter that much
* Primary fire is the same, while second is just a strong and slow swing attack
* Press the FIST key and you get an attack that makes enemies drop health goodies
>8th slot: Fire axe
* Doom RPG's axe, which normally had a black head and yellow handle, but who cares
* Primary/second fire: Slow melee attack that makes enemies bleed and drop health for a while, but zombie types die instantly
* Can destroy barrels without exploding them, this can be usefull

==INVENTORY==
This mod has one like Heretic and items use a shared ammo system, so if you get X you also get Y but using X also wastes use for Y.
You get 25 "ammo" and you can use these items during normal gunplay (Think of it like Doom Eternal's shoulder cannon before that was a thing) but there's a less than a second delay break when you use something

>HAND GRENADE
* Based off D3's grenade but how it works is D4's frag grenade, but it still explodes on impact with foes
* Spawns next to rocket ammo
>SYPHON GRENADE
* D4 item that sort of stuns enemies, while sucking their health to heal the player
* Spawns next to Plasma ammo
>TELSA ROCKET
* D4 MP item that is thrown at the air and travels to one direction, while travelling foes nearby
* When it hits walls it explodes and that can hurt
* Spawns next to Plasma ammo
>DOG COLLER
* Doom RPG item that spawns next to bullet ammo
* You shoot a yellow thingy that turns dog enemies into melee weapons
* These dog guns can gain armor points from hurting enemies and if you're tired of this, you can throw them at enemies and they'll go boom
* Originally, you could have used them as shields
>WALLSHILED
* D4 MP item that spawns near health
* It creates a solid blue transparent wall (May or may not resemble shiled from D4 possessed security) that stops most enemies attacks, while yours go right through it
>HOLOGRAM
* D4 item that creates a holographic image of the player to distract enemies from the real you
* Spawns near Hastespheres
>KINETIC MINE
* D4 MP DLC mines that pawn near backpacks
* These mines can be put on walls/ceilings/floors and take less than a second to activate
* When they detect a target, them jump/fly to them and explode
* If they don't detect them, however, they just take like 20 "ticks" to deactive and become pickable again
>ARTIFACT
* Doom 3 Resurection of Evil's magic heart that spawns near Plasma guns but only if you got a BFG
* When you use them, they slow down time for 5 seconds, giving you lots of opportunities

==ENEMIES==
Much like weapons and items, they get progress randomization too and some monsters are combinations of things too. Because some enemy types are just redesigns of the same monster, they take Doom RPG enemies from otherwise palette swaps
>ZOMBIEMAN
* He has new/changed sounds and hitscan replaced with tracers and these changes apply to other zombie types
>HELL RAZER
* D4 monster who has more health than Zombieman and charges a laser that deals continuous damage
>SHOTGUN GUY
* See zombieman
>Z SEC
* Based off D3's Z Sec, with a shotgun, rifle zombie's helmet and the ability to roll, which according to Doomwiki, is from the pistol zombie
* Has D64/PSX sounds
>FORMER LIEUTENANT
* Works as a replacement for the normal chaingunner, but his name and blue armor represent a blue zombieman from DRPG, while he carries the assault rifle
>FORMER COMMANDO
* Carries the chaingun and his red armor indicate he's in fact the Doom 2 heavy weapon dude, despite the differences
>FORMER ASSASSIN
* Based off Doom 3's commando zombies (both types), so he has both a chaingun and a tentacle arm that can slap you hard enough you're thrown to other directions
* Lines may as well be beta Doom 3 stuff
>IMP
* Mostly unchaged but he has one new sound when hurt
>NIGHTMARE IMP
* Can replace Imp in darker areas and he works faithfully enough (Faster, transparent, faster projectiles) he even gets specific spawns in Consolation Prize's D64 maps
>IMP LORD
* D4 imp, who is faster and can teleport as an homage to the cancelled D4
* Name may be taken from orange DRPG imp
>PINKEY AND SPECTRE
* These two may be unchanged for what i know
>HELLHOUND
* DRPG dog enemy who works as a faster, but low health Pinkey, that can be a weapon with the Dog Collar
>DEMONDOG
* Same as above but blue and strafes a lot
>CERBERUS
* Another dog, this one is red and jumps around
* These dop types seem to use Wolfenstein 3D/Quake sounds, with Cerberus being a Quake Fiend reference
* Dog enemies may also have a high chance to replace Pinkies if zombie types are nearby
>BULL DEMON
* D3 Pinky named after DRPG yellow pinky, who has a charge attack inspired by D4 pinky
>NIGHTMARE SPECTRE
* Exclusive PSX enemy that can replace Spectre in darker areas and as expected, he's faster and has more health
* He uses D64 Pinky sprites but the blue/inverted color effect still makes him Nightmare Spectre
>TRITES
* Doom 3 spiders who can replace Spectres in darker areas
* Three of them spawn at once and they're small, fast melee monsters who at times can attach to the ceiling and walking on it (Inspired by a Strife enemy)
* They can only spawn in early levels before never showing up again
* Sometimes they don't show up at all
* They have their own special toggle option due to possible arachnophobia
>SAWCUBUS
* D2RPG chainsaw enemy, based off the green variant Great Sawcubus (Using the Java look)
* Replaces Spectre and does the chainsaw attack on you (Duh)
* If gibbed, he may drop a chainsaw
* Sounds are meant to be Doom 3 Sawyer related, but they might be Beta D3 stuff
>CACODEMON
* Unchanged but he can be gibbed and drop some unique gore sprites
>MALWRATH
* D64 Caco named after yellow DRPG Caco that shoots three balls at once
* May or may not D3 related sounds
>WRETCHED
* D4 Caco named after DRPG blue Caco who has a tongue attack (Taken from D4 MP) similar to Former Assassin's tentacle arm (I think this tentacle/tongue thing may be based off Strife's Loremaster)
>PAIN ELEMETANL
* If you get too close, he can bite you now
>BEHOLDER
* Green PE from DRPG who lacks arms so he looks more unique
* Spews smaller LS's named Forgotten Ones
>RAVOHART
* Doom 64 PE named after DRPG blue PE who spits two LS's at once
>LOST SOUL
* Sprites are changed so his flames look more "authentic"
>PHANTOM
* Cut/alpha LS sprites with green flames (Possibly to reference the Invulnerability sphere since it used his sprites)
* Named after green LS from DRPG and uses D4 sounds (They were altered to sound robotic)
* Can strafe, has a projectile attack and has higher infighting chance
>FORGOTTEN ONES
* Smaller LS's meant to represent human skulls named after an LS from D3Resurrection of Evil
* They're small and swarm around, while only originating from Beholder
>MANCUBUS
* His attack shakes the screen for some reason
>BEHEMOTH
* D64 Manc named after DRPG blue Manc, who spits travelling streams of flames based off D4's Manc's flamethrower
* May use D3 sounds
>CYBER MANCUBUS
* D4 Manc with more health, whose (Continuously) shoots green sticky stuff that sticks to the level and explodes shortly after
* Unique death animation where he explodes shortly after dying and this only harms enemies
>ARACHNOTRON
* His attack may use a different sound
>SPIBORG
* D64 Arachno who's name is made up due to lack of RPG Arachnos
* His attack his charging a powerfull fast Plasma ball
* Originally in D64, he shoots two plasma balls five times and charging a Plasma ball is more of a D4 possessed soldier thing
>REVENANT
* Uses PSX Doom sounds but i'm not sure about the beeping homing rocket noise
>FIEND
* D4 Revenant (He's pretty much a regular Rev with fleshy/bloody bones right now) who can shoot streams of micromissiles and jump with jetpack
* He still has Rev's normal attacks and is named after blue Rev from DRPG
>ARCHVILE
* If you kill him, he drops BFG ammo
>SUMMONER
* D4's take on Archie who has less health than him, but still retains his attacks
* Summoner can teleport and summon Unwilling, by throwing D2 Spawn cubes in the air and let them drop in the floor, to spawn said Unwilling
* Also drops BFG ammo after and i don't know about his alert noise
* According to the normal randomization process, he'd possibly the last enemy you'll encounter
>UNWILLING
* Inspired by zombie type enemies from D4/3, they can also throw blood pieces like Quake 1's Zombies
* They're weak as fuck too
>HELLKNIGHT
* Based off D4, by design and ground slam ability, while using D3 sound for alert noise and retaining D2 death sound
>BARON OF HELL
* D4 version, who's bigger than HK
* He has a stronger ground slam (It forms like 4 red triangles that hurt for a bit) and shoots red fireballs that split into four green fireballs
>CYBERDEMON
* D64 sprites and D3 sounds
* Can strafe, shoot while walking and may have more health
* Slide ability from D4 and can kick you if close enough (May be a Doom bible thing)
* Slide ability may also somewhat take something from Heretic's Maulotaur (Maybe)
>SPIDER MASTERMIND
* Unique design meant to combine old and new versions of the monster, while looking like it's coming out of D64
* Main attack is rapid fire Plasma balls
* Second attack is shooting fireballs to different directions through the floor, possibly based off D64 Mother Demon's fire attack or a D4 attack where she'd shock the floor with blue lightning (I think it even uses that sound)
* She also does a pose from a cut magic attack sprite in the second attack

==ITEMS==
HEALTH: Health bonus is just a shinier vial with some D4 sound, simpick is blue colored D64 sprite and medikit is a D4 health pick up, possibly using a DRPG sound
ARMOR: Bonus is a D4 armor shard, green armor is D2RPG sprite (Name is Security Armor, possible D3 reference) and megaarmor is a D4 pick up painted blue
BACKPACK: Uses D64 sprite and has a D3 sound, since there was a backpack there
BULLETS AMMO: D64 clip sprite and a classic ammo box still kept
SHELL AMMO: D64 sprites with slight alterations
ROCKET AMMO: Single rocket from D64 and a box that may be a bit original (But still somewhat resembling D64?)
CELL AMMO: Both pick ups look like a mix of classic Doom and 64 sprites
ARGENT CORE: BFG ammo spawning near either Plasma ammo or dropped by dead Archies while its design is unique but fitting
LOOT: Already explanied above somewhere
RADSUIT: Design is a mix of classic Doom radsuit and D3 Hazmat suit, while icon was the power up's design in D64
COMPUTER AREA MAP: Design is D3'S PDA, sounds are possibly D4 related (There was a map machine there) but maps on screen? Maybe just random classic Doom maps (There's also a joke in the codex about Doom being ported into devices and a reference to the Doom bible related title "Evil Unleashed")
INVULNERABILITY: D64 sprites but brighter and with yellow eyes, while the blue filter is a reference to the power up's effect in the GBA port
SOULSPHERE: D64 sprites but brighter to resemble classic Doom and pick up sound seems to be based off both D1/2 and Megahealth from D4
MEGASPHERE: The Manc inside the sphere is based off D4 and pick up sound is Megahealth, again, from D4
BERSERK: Design is the BFG edition "pill in the box" edit, sound is a little D4 screech related to those trial runes and icon is an angry eye from D2RPG; Gameplay wise it makes the player's fists do more damage and faster (Maybe enemies drop more health) but it's timed; Traditional Berserk makes Berserk last for a level and i guess that's how the fist sort of becomes an ingame weapon (Shares same slot with pistol)
QUAD DAMAGE: D4/Quake power up whose design is a purple sphere with a Rev inside it and it obviously increases damage for your weapons but if Traditional Berserk is on, they're gone; They have health near them because they replace Berserk which normally gives you 100 health
HASTESPHERE: D4/Quake 3 power up whose design is a red sphere with Doomguy's helmet (D64 Megapshere) and it obviously makes you run fast
LIGHT AMP VISER: Design is D64 sprite but slightly altered and icon is a bit of its D64 sprite, not sure about sound. It also has green lenses, possibly to reference a cut night vision from early Doom prototypes, which may have lead to GZDoom's night vision mode


Not everything is covered and there's some accidental misinformation and poor grammar, but i just thought this would have been interesting