Mordenkainen Presents Monsters of the Multiverse contains revamped stat blocks for 260 monsters previously published in previous Dungeons & Dragons 5E books. The list was compiled by YouTuber Bob Worldbuilder based on some blurry screenshots originally shared by Nerd Immersion (see the video below). I have transcribed it here for convenience.
	
	
		
			
				
					
						
					
				
			
			
				
					
						
							
						
					
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			D&D 5E - List of All 33 Races in Mordenkainen's Monsters of the Multiverse
Mordenkainen Presents Monsters of the Multiverse contains 33 races compiled from previous Dungeons & Dragons books.    Aarackocra Assimar Bugbear Centaur Changeling Deep Gnome Duergar Eladrin Fairy Firbolg Genasi, Air Genasi, Earth Genasi, Fire Gennasi, Water Githyanki Githzerai Goblin Goliath...
				
						
					
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				- Abishai (Black, Blue, Green, Red, White)
 - Alhoon
 - Alkilith
 - Allip
 - Amnizu
 - Annis Hag
 - Archdruid
 - Archer
 - Armanite
 - Astral Deadnought
 - Babau
 - Bael
 - Balhannoth
 - Banderhobb
 - Baphomet
 - Bard
 - Barghest
 - Berbalang
 - Bheur Hag
 - Blackguard
 - Bodak
 - Boggle
 - Boneclaw
 - Bulezau
 - Cadaver Collector
 - Canoloth
 - Catoblepas
 - Cattle (Aurochs, Ox, Stench Kow, Deep Rothe)
 - Cave Fisher
 - Champion
 - Chitine
 - Choker
 - Choldrith
 - Clockwork (Bronze Scout, Iron Cobra, Oaken Bolter, Stone Defender)
 - Cloud Giant Smiling One
 - Corpse Flower
 - Cranium Rat, Swarm of Cranium Rat
 - Darkling, Darkling Elder
 - Death Kiss
 - Deathlock, Deathlock Mastermind, Deathlock Wight
 - Deep Scion
 - Demogorgon
 - Derro, Derro Savant
 - Devourer
 - Dhergoloth
 - Dinosaurs (Brontosaurus, Deinonychus, Dimetrodon, Hadrosaurus, Quetzalcoatlus, Stegosaurus, Velociraptor)
 - Dolphin, Dolphin Delighter
 - Draegloth
 - Drow (Arachnomancer, Favored Consort, House Captain, Inquisitor, Matron Mother, Shadowblade)
 - Duergar (Despot, Kavalrachni, Mind Master, Soulblade, Stone Guard, Warlord, Xarrorn, Hammerer, Screamer)
 - Dybbuk
 - Eidolon
 - Eladrin (Autumn, Spring, Summer, Winter)
 - Elder Brain
 - Elder Tempest
 - Elemental Myrmidon (Air, Earth, Fire, Water)
 - Fire Giant Dreadnought
 - Firenewt (Warrior, Warlock of Imix)
 - Flail Snail
 - Flind
 - Fraz-Urb'luu
 - Froghemoth
 - Frost Giant Everlasting One
 - Frost Salamander
 - Gauth
 - Gazer
 - Geryon
 - Giant Strider
 - Giff
 - Girallon
 - Githyanki (Gish, Kith'rak, Supreme Commander, Anarch, Enlightened)
 - Gnoll (Flesh Gnawer, Hunter, Witherling)
 - Gray Render
 - Grazz't
 - Grung (Elite Warrior, Wildling)
 - Guard Drake
 - Hellfire Engine
 - Hobgoblin (Devastator, Iron Shadow)
 - Howler
 - Hutijin
 - Hydroloth
 - Juiblex
 - Ki-Rin
 - Kobold (Dragonshield, Inventor, Scale Sorcerer)
 - Korred
 - Kraken Priest
 - Kruthik (Hive Lord, Adult, Young)
 - Leucrotta
 - Leviathan
 - Martial Arts Adept
 - Marut
 - Master Thief
 - Maurezhi
 - Maw Demon
 - Meazel
 - Meenlock
 - Merregon
 - Merrenoloth
 - Mindwitness
 - Moloch
 - Molydeus
 - Morkoth
 - Mouth of Grolantor
 - Nabassu
 - Nagpa
 - Narzugon
 - Neogi, Neogi Hatchling, Neogi Master
 - Neothelid
 - Nightwalker
 - Nilbog
 - Nupperibo
 - Oblex (Spawn, Adult, Elder)
 - Ogre (Battering Ram, Bolt Launcher, Chain Brute, Howdah)
 - Oinoloth
 - Orcus
 - Orthon
 - Phoenix
 - Quickling
 - Redcap
 - Retriever
 - Rutterkin
 - Sea Spawn
 - Shadar Kai (Gloom Weaver, Shadow Dancer, Soul Monger)
 - Shadow Mastiff, Shadow Mastiff Alpha
 - Shoosuva
 - Sibriex
 - Skulk
 - Skull Lord
 - Slithering Tracker
 - Shadowsworn (The Angry, The Hungry, The Lonely, The Lost, The Wretched)
 - Spawn of Kyuss
 - Star Spawn (Grue, Hulk, Lava Mage, Mangler, Seer)
 - Steeder (Female, Male)
 - Steel Predator
 - Stone Cursed
 - Stone Giant Dreamwalker
 - Storm Giant Quintessent
 - Swarm of Rot Grubs
 - Swachbuckler
 - Sword Wraith (Commander, Warrior)
 - Tanarukk
 - Titivilus
 - Tlincalli
 - Tortle
 - Turtle Druid
 - Trapper
 - Troll (Dire, Rot, Spirit, Venom)
 - Ulitharid
 - Vampiric Mist
 - Vargouille
 - Vegepygmy, Vegepygmy Chief, Vegepygmy Thorny
 - War Priest
 - Warlock (of the Archfey, Fiend, Great Old One)
 - Warlord
 - Wastrilith
 - Wizard (Apprentice, Abjurer, Conjurer, Diviner, Enchanter, Evoker, Illusionist, Necromancer, Transmuter)
 - Wood Woad
 - Xvart, Xvart Warlock of Raxivort
 - Yagnoloth
 - Yeenoghu
 - Yeah Hound
 - Yuan-ti (Anathema, Broodguard, Mind Whisperer, Nightmare Speaker, Pit Master)
 - Zaratan
 - Zariel
 - Zuggtmoy