If an effect instructs a player to choose a subtype, that player must choose one, and only one, existing subtype, and the subtype he or she chooses must be for the appropriate card type. For example, the player can't choose a land type if an instruction requires choosing a creature type.
Example: When choosing a creature type, "Merfolk" or "Wizard" is acceptable, but "Merfolk Wizard" is not. Words like "artifact," "opponent," "Swamp," or "truck" can't be chosen because they aren't creature types.

Advisor, Aetherborn, Ally, Angel, Antelope, Ape, Archer, Archon, Artificer, Assassin, Assembly-Worker, Atog, Aurochs, Avatar, Badger, Barbarian, Basilisk, Bat, Bear, Beast, Beeble, Berserker, Bird, Blinkmoth, Boar, Bringer, Brushwagg, Camarid, Camel, Caribou, Carrier, Cat, Centaur, Cephalid, Chimera, Citizen, Cleric, Cockatrice, Construct, Coward, Crab, Crocodile, Cyclops, Dauthi, Demon, Deserter, Devil, Djinn, Dragon, Drake, Dreadnought, Drone, Druid, Dryad, Dwarf, Efreet, Elder, Eldrazi, Elemental, Elephant, Elf, Elk, Eye, Faerie, Ferret, Fish, Flagbearer, Fox, Frog, Fungus, Gargoyle, Germ, Giant, Gnome, Goat, Goblin, God, Golem, Gorgon, Graveborn, Gremlin, Griffin, Hag, Harpy, Hellion, Hippo, Hippogriff, Homarid, Homunculus, Horror, Horse, Hound, Human, Hydra, Hyena, Illusion, Imp, Incarnation, Insect, Jellyfish, Juggernaut, Kavu, Kirin, Kithkin, Knight, Kobold, Kor, Kraken, Lamia, Lammasu, Leech, Leviathan, Lhurgoyf, Licid, Lizard, Manticore, Masticore, Mercenary, Merfolk, Metathran, Minion, Minotaur, Mole, Monger, Mongoose, Monk, Monkey, Moonfolk, Mutant, Myr, Mystic, Naga, Nautilus, Nephilim, Nightmare, Nightstalker, Ninja, Noggle, Nomad, Nymph, Octopus, Ogre, Ooze, Orb, Orc, Orgg, Ouphe, Ox, Oyster, Pegasus, Pentavite, Pest, Phelddagrif, Phoenix, Pilot, Pincher, Pirate, Plant, Praetor, Prism, Processor, Rabbit, Rat, Rebel, Reflection, Rhino, Rigger, Rogue, Sable, Salamander, Samurai, Sand, Saproling, Satyr, Scarecrow, Scion, Scorpion, Scout, Serf, Serpent, Servo, Shade, Shaman, Shapeshifter, Sheep, Siren, Skeleton, Slith, Sliver, Slug, Snake, Soldier, Soltari, Spawn, Specter, Spellshaper, Sphinx, Spider, Spike, Spirit, Splinter, Sponge, Squid, Squirrel, Starfish, Surrakar, Survivor, Tetravite, Thalakos, Thopter, Thrull, Treefolk, Triskelavite, Troll, Turtle, Unicorn, Vampire, Vedalken, Viashino, Volver, Wall, Warrior, Weird, Werewolf, Whale, Wizard, Wolf, Wolverine, Wombat, Worm, Wraith, Wurm, Yeti, Zombie, and Zubera.