Originally, in Alpha, creature types were largely used for flavor-related reasons. This was continued until Fallen Empires, when creatures types had in-game mechanical implications. The first block in which creature types mattered was Tempest, particularly via the Licids and Slivers, both of which creature types shared a mechanical identity among its creature cards.
Prior to the Grand Creature Type Update, creature types were only changed when a card was reprinted. This policy was straightforward when only core sets and regular expansions were considered. However it became quite complicated when digital sets on Magic Online (such as the release of the Mirage block or Masters Edition) were considered "reprints". Offbeat reprints found in Coldsnap theme decks and the timeshifted cards in Time Spiral added to the confusion.
Updates before the Grand Update
- Aesthir became Bird (Wild Aesthir) 
- Archer became Soldier (Femeref Archers) (other archers Oracle only; to be reversed in the Grand Update)
- Autocrat became Minion (Sengir Autocrat) (in Time Spiral changed again into Human)
- Cyclops became Giant (Hulking Cyclops) (later reversed)
- Dead became Skeleton (Kjeldoran Dead)
- Evil-Eye became Horror (Evil Eye of Orms-by-Gore) (in Time Spiral changed again into Eye)
- Falcon became Bird (Mesa Falcon) (change in Zephyr Falcon and other falcons Oracle only).
- Folk of An-Havva became Townsfolk (Oracle only; later to be changed into Human)
- Gorilla became Ape (Gorilla Chieftain)
- Gorilla-Pack became Ape (Gorilla Pack; Oracle only)
- Hunter became Minion (Abyssal Hunter)
- Lost-Soul became Minion (Lost Soul) (in the Grand Update, Spirit would be added)
- Mana Bird became Bird (Birds of Paradise)
- Nature-Spirit became Elemental (Maro)
- Nymph became Dryad (Shanodin Dryads)
- Pigeon became Bird (Carrier Pigeons; Oracle only)
- Python became Snake (Python)
- Rider became Elf (Elven Riders)
- Rooster became Chicken (Zodiac Rooster; Oracle only)
- Undead became Horror or Wraith (Hidden Horror, Odylic Wraith)
- Wildcat became Cat Warrior (Uktabi Wildcats) (in this case Warrior was eliminated again in 7th Edition)
- Wyvern became Drake (Cerulean Wyvern; Oracle only)
- Rag-Man became Minion (Rag Man)
- Scavenger-Folk became Scavenger (Scavenger Folk) (changed again to Human in the Grand Update)
- Tiger became Cat (Sabretooth Tiger)
- Splinter-tokens became Sprite-tokens (Splintering Wind; Oracle only).
Champions of Kamigawa
- Behemoth became Elemental (Llanowar Behemoth)
- Cheetah became Cat (King Cheetah) (other Cheetahs unaffected)
- Clone became Shapeshifter (Clone)
- Force became Elemental (Force of Nature)
- Hell's Caretaker became Horror (Hell's Caretaker)
- Lion became Cat (Savannah Lions)
- Monkey became Ape (Tree Monkey, Zodiac Monkey)
- Nekrataal became Human (Nekrataal)
- Will-O'-The-Wisp became Spirit (Will-O'-The-Wisp)
Mirage online release
- Ancestor became Human Cleric (Auspicious Ancestor)
- Dreadnought added to Phyrexian Dreadnought
- Mantis became Insect (Giant Mantis)
- Martyr became Cleric (Vigilant Martyr)
- Meerkat became Mongoose (Karoo Meerkat)
- Swarm became Insect (Locust Swarm)
- Tombspawn became Zombie (Tombstone Stairwell)
- Wood became Plant (Jungle Patrol)
Ravnica: City of Guilds
- Introduction of the Weird type
- Ghoul became Zombie (Ashen Ghoul) (other Ghouls not affected) 
- Mammoth became Elephant (Woolly Mammoths) (other Mammoths not affected)
- Mistfolk became Illusion (Mistfolk)
- Warthog became Beast (Giant Warthog)
Visions online release
- Butterfly became Insect (Giant Caterpillar)
- Chimera added to the Chimeras
- Hippopotamus became Hippo (Pygmy Hippo)
- Lichenthrope became Plant Fungus (Lichenthrope)
- Lion became Cat (Mtenda Lion and Jamuraan Lion)
- Mindsucker became Horror (Urborg Mindsucker)
- Necrosavant became Zombie Giant (Necrosavant)
- Wildebeest became Beast (Stampeding Wildebeests) (later altered to Antelope)
- Warthog became Boar (Warthog)
Time Spiral "Timeshifted"
- Kor type added (Looter il-Kor) 
- Cavalry became Knight (Moorish Cavalry)
- Dandân became Fish (Dandân)
- Dervish became Monk (Whirling Dervish)
- Dauthi type added (Dauthi Slayer)
- Eye was (re)introduced with Evil Eye of Urborg. Accordingly, Evil Eye of Orms-by-Gore was changed again.
- Flying-Man became Human (Flying Men)
- Gaea's Liege became Avatar (Gaea's Liege)
- Hunter became Cleric (Witch Hunter)
- Mosquito became Insect (Swamp Mosquito)
- Ship became Spirit (Ghost Ship). Other changes from Ship were realized in the Grand Update.
- Sindbad became Human (Sindbad)
- Soltari type added (Soltari Priest)
- Sorcerer became Wizard (Ovinomancer)
- Sprite-tokens reverted to Splinter-tokens (Splintering Wind)
- Squire became Soldier (Squire)
- Taskmaster became Kobold (Kobold Taskmaster)
- Uncle-Istvan became Human (Uncle Istvan)
- Archaeologist became Artificer (Argivian Archaeologist)
- Avenger became Soldier (Righteous Avengers)
- Brother became Human (Brothers of Fire)
- Ball-Lightning became Elemental (Ball Lightning)
- Doppelganger became Shapeshifter (Vesuvan Doppelganger)
- Eater became Horror (Eater of the Dead)
- Fallen became Zombie (The Fallen)
- Lemure became Spirit (Hyalopterous Lemure)
- Mist became Elemental (Hungry Mist)
- Mob became Human (Angry Mob)
- Poison-Snake became Snake (Serpent Generator)
- Preacher became Cleric (Preacher)
- Raider became Warrior (Erg Raiders)
- Shadow became Spirit (Nether Shadow)
- Singing-Tree became Plant (Singing Tree)
- Speaker became Cleric (Death Speakers)
- Strider became Yeti (Shambling Strider)
- Toad became Frog (Chub Toad)
- Tortoise became Turtle (Giant Tortoise)
- Villain became Beast (Spinal Villain)
- War-Rider became Warrior (Varchild's War-Riders)
- Witch became Wizard (Cuombajj Witches)
Weatherlight online release
- Aboroth became Elemental (Aboroth)
- Avizoa became Jellyfish (Avizoa)
- Barishi became Elemental (Barishi)
- Gatekeeper became Horror (Abyssal Gatekeeper)
- Peacekeeper became Human (Peacekeeper)
- Thundermare became Elemental Horse (Thundermare)
- Vulture became Bird (Wake of Vultures) (other Vultures not affected)
Prelude to the Grand Creature Type Update
Mirrodin was the first set to implement the race-class model and along with it most notably the Human subtype was introduced. At that time it was an open question whether creature types on existing cards should be changed. In the end, the decision was made in favor of having consistent creature types in the core set (Ninth Edition).
While a mass errata was ruled out in the beginning, a couple of years later Aaron Forsythe actually hinted at an Oracle update. Since Lorwyn block had a tribal theme, it was the perfect opportunity to realize those "sweeping changes."
Grand Creature Type Update
The Grand Creature Type Update was a mass update of creature types, as part of the regular Oracle update for Lorwyn in October 2007. With 1197 affected cards, it represented the bulk of the changes. The update ranks as one of the biggest changes to the Oracle (the update for Ninth Edition has been comparable in scope, changing hundreds of local enchantments to Auras).
First and foremost a lot of creatures got the Human subtype, and some cards got other races like Dryad, Dauthi, Kor, or Merfolk. Another objective was making creatures conform to the modern race-class model. Creatures that lacked an obvious class got a class. Additionally, 146 obsolete creature types were removed, most of them being one-offs such as "Ali-from-Cairo" or "People-of-the-Woods". Un-sets types were also dropped. Eight new types were added. For flavor reasons, Nameless Race became the only creature without a creature type.
Also, creatures without creature types got creature types. There were three types of cards that lacked creature types. 1) Prior to the Champions of Kamigawa set, Legend was a creature type. Most legendary creatures were printed as "Summon Legend" or "Creature — Legend," and had no further creature types. 2) Many artifact creatures did not have subtypes. 3) Some cards that self-animate did not list the creature types they gained.
The changes were controversial, as seen on the Magic the Gathering forums. Players either disagreed with the necessity of the update or whether the individual changes were right. R&D now considers the Grand Creature Type Update to have been a mistake. Too many cards do not do what they say.
Abomination, Aladdin, Albatross, Alchemist, Ali-Baba, Ali-from-Cairo, Alligator, Ambush-Party, Ant, Asp, Bandit, Banshee, Bee, Being, Bodyguard, Brownie, Bull, Bureaucrat, Caravan, Carnivore, Carriage, Cave-People, Cheetah, Chicken, Child, Clamfolk, Cobra, Constable, Cow, Crusader, Designer, Devouring-Deep, Dinosaur, Dog, Donkey, Dragonfly, Drill-Sergeant, Eel, Effigy, El-Hajjâj, Enchantress, Entity, Erne, Essence, Exorcist, Expansion-Symbol, Farmer, Fiend, Frostbeast, Fungusaur, Gaea's-Avenger, Gamer, General, Ghost, Ghoul, Guardian, Gus, Gypsy, Harlequin, Heretic, Hero, Hipparion, Hornet, Horseman, Hyena, Infernal-Denizen, Inquisitor, Island-Fish, Jackal, Keeper, Kelp, King, Lady-of-Proper-Etiquette, Legend, Legionnaire, Leper, Lord, Lurker, Lycanthrope, Mage, Maiden, Mammoth, Marid, Master, Medusa, Merchant, Mime, Minor, Miracle-Worker, Mold-Demon, Monster, Mummy, Murk-Dweller, Nameless-Race, Narwhal, Niall-Silvain, Noble, Paladin, Paratrooper, Penguin, People-of-the-Woods, Phantasm, Pig, Pikemen, Pixie-Queen, Poltergeist, Pony, Priest, Pyknite, Ranger, Robber, Roc, Rock-Sled, Sage, Scavenger, Shark, Ship, Shyft, Sister, Smith, Sorceress, Spuzzem, Spy, Stangg-Twin, Tactician, Tarpan, Teddy, Thief, The-Biggest-Baddest-Nastiest-Scariest-Creature-You'll-Ever-See, Titan, Townsfolk, Tracker, Twin, Viper, Vulture, Waiter, Walking-Dead, Wasp, Whippoorwill, Wight, Wiitigo, Wirefly, Wolverine-Pack, Wolves-of-the-Hunt, Wretched.
The "Grand Creature Type Update" Update
- The recently introduced type Anemone was dropped again. Glowing Anemone was changed back to Beast and received the added Jellyfish type.
- Gremlin was dropped in favor of Ouphe (Phyrexian Gremlins). This was later reversed.
- Spawn became Elemental (Elder Spawn) This was later reversed (and Spawning Pit from Darksteel always kept producing spawn tokens).
- Hyena made a return (Gibbering Hyenas)
After the "Grand Creature Type Update" Update
- Introduction of the Noggle type.
- Introduction of the Siren type.
Rise of the Eldrazi
- Introduction of the Eldrazi type
- The Spawn type was reinvented for tokens created by several cards from Rise of the Eldrazi. Elder Spawn wasn't changed back to its original type but remained an Elemental, until the release of Innistrad.
- Egg became Bird. When the M11 card Roc Egg was printed, the creature type "Egg" was decommissioned and Rukh Egg was changed accordingly.
Scars of Mirrodin
- Introduction of the Hippogriff type.
- With the re-introduction of the Gremlin creature type in Mirrodin Besieged (Flensermite), Phyrexian Gremlins changed back from Ouphe to Gremlin.
- Introduction of the Germ type.
- Introduction of the Praetor type.
- Introduction of the Werewolf type.
- Introduction of the types God and Sable.
- Re-introduction of the type Nymph.
- For Challenge Decks the card type Hero, the subtype Head and supertype Elite were used, but not added to the comprehensive rules.
Journey into Nyx
- Introduction of the Lamia type.
- For Challenge Decks the Reveler subtype was used, but again not added to the comprehensive rules.
Khans of Tarkir
- Introduction of the Naga type.
Battle for Zendikar
Shadows over Innistrad
- Introduction of the Mole type.
- Introduction of the Aetherborn, Pilot, and Servo creature types.
- Re-introduction of the Monkey creature type.
- R&D changes their stance that every supported creature type mentioned in the card name has to be on the card. Therefore, Quicksmith Rebel and others don't have the Rebel type.
- Re-introduction of the Jackal type.
- Unstable (re)introduced many types, but these are not legal and don't appear in the comprehensive rules.
- Introduction of the Azra type.
Global Series: Jiang Yanggu & Mu Yanling
- Introduction of the Pangolin type.
Core set 2019
- Re-introduction of the Egg type.
War of the Spark
- Introduction of the Army type.
- Introduction of the Sculpture type.
Throne of Eldraine
Ponies: The Galloping
Theros: Beyond Death
Ikoria: Lair of Behemoths
Core Set 2021
- Introduction of the Phyrexian type
Strixhaven: School of Mages
- Introduction of the Inkling and Fractal types.
- Pests appear for the first time outside of Mirrodin and as non-artifact ctreatures..
Modern Horizons 2
Dungeons & Dragons: Adventures in the Forgotten Realms
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- Sixth Edition Oracle. October 5, 1999. Retrieved July 23, 2013.
- Mark Rosewater (October 04, 2004). "Change For the Better". magicthegathering.com. Wizards of the Coast.
- "Ninth Edition Frequently Asked Questions : Wizards of the Coast". June 30, 2005. Retrieved July 23, 2013.
- Magic Arcana (July 31, 2006). "Mistform Ultimus Watch: Coldsnap Edition". magicthegathering.com. Wizards of the Coast.
- Magic Arcana (October 03, 2006). "Mistform Ultimus Watch – Time Spiral". magicthegathering.com. Wizards of the Coast.
- Aaron Forsythe (July 16, 2004). "Classifying Samite Healers". magicthegathering.com. Wizards of the Coast.
- Randy Buehler (November 29, 2002). "Human Nature". magicthegathering.com. Wizards of the Coast.
- Aaron Forsythe (August 24, 2007). "Looking Back to the Future". magicthegathering.com. Wizards of the Coast.
- Mark Gottlieb (September 26, 2007). "Lorwyn Update Bulletin". magicthegathering.com. Wizards of the Coast.
- "The Grand Creature Type Update (and other Rules Updates) - MTG Salvation Forums". Retrieved July 23, 2013.
- Mark Rosewater (March 16, 2014). "Is the number of cards that would have to be rewritten really more than the Grand Creature Type Update?". Blogatog. Tumblr.
- Mark Rosewater (March 17, 2014). "The Grand Creature Update was a mistake? Why?". Blogatog. Tumblr.
- Mark Rosewater (May 15, 2013). "Is retroactively applying creature types considered "functional errata"?". Blogatog. Tumblr.
- Mark Rosewater (August 01, 2017). "Why is it that creature types get a pass, given that they do have gameplay repercussions?". Blogatog. Tumblr.
- Mark Gottlieb (January 16, 2008). "Morningtide Update Bulletin". magicthegathering.com. Wizards of the Coast.
- Matt Tabak (January 15, 2015). "Fate Reforged Update Bulletin — Oracle Text". magicthegathering.com. Wizards of the Coast.
- Mark Rosewater (January 28, 2017). "Is Rebel no longer a supported creature type?". Blogatog. Tumblr.
- Eli Shiffrin (September 27, 2019). "Throne of Eldraine Oracle Changes". magicthegathering.com. Wizards of the Coast.
- Eli Shiffrin (June 20, 2020). "Core Set 2021 and Jumpstart Release Notes". magicthegathering.com. Wizards of the Coast.