mythical being - an imaginary being of myth or fable

legendary creature - unverifiable but popularly accepted as possibly factual

monster - an imaginary creature usually having various human and animal parts

amphisbaena - (classical mythology) a serpent with a head at each end of its body

basilisk - (classical mythology) a serpent (or lizard or dragon) able to kill with its breath or glance

centaur - (classical mythology) a mythical being that is half man and half horse

Cerberus, hellhound - (Greek mythology) 3-headed dog guarding the entrance to Hades; son of Typhon

Chimaera, Chimera - (Greek mythology) fire-breathing she-monster with a lion's head and a goat's body and a serpent's tail; daughter of Typhon

cockatrice - monster hatched by a reptile from a cock's egg; able to kill with a glance

dragon, firedrake - a creature of Teutonic mythology; usually represented as breathing fire and having a reptilian body and sometimes wings

Geryon - (Greek mythology) a mythical monster with three heads that was slain by Hercules

Gorgon - (Greek mythology) any of three winged sister monsters and the mortal Medusa who had live snakes for hair; a glance at Medusa turned the beholder to stone

griffin, gryphon - winged monster with an eagle-like head and body of a lion

Harpy - (Greek mythology) vicious winged monster; often depicted as a bird with the head of a woman

Hydra - (Greek mythology) monster with nine heads; when struck off each head was replaced by two new ones; "Hydra was slain by Hercules"

leviathan - monstrous sea creature symbolizing evil in the Old Testament

mantichora, manticora, manticore, mantiger - a mythical monster having the head of man (with horns) and the body of a lion and the tail of a scorpion

Minotaur - (Greek mythology) a mythical monster with the head of a bull and the body of a man; slain by Theseus

Nemean lion - (Greek mythology) an enormous lion strangled by Hercules as the first of his 12 labors

Python - (Greek mythology) dragon killed by Apollo at Delphi

roc - mythical bird of prey having enormous size and strength

salamander - reptilian creature supposed to live in fire

Sphinx - (Greek mythology) a riddling winged monster with a woman's head and breast on a lion's body; daughter of Typhon

troll - (Scandanavian folklore) a supernatural creature (either a dwarf or a giant) that is supposed to live in caves or in the mountains

Typhoeus - (Greek mythology) son of Gaea and Tartarus who created the whirlwinds; had a terrifying voice and 100 dragon heads that spurted fire

Typhon - (Greek mythology) a monster with a hundred heads and one of the whirlwinds; son of Typhoeus and Echidna; father of Cerberus and the Chimera and the Sphinx

lycanthrope, werewolf, wolfman - a monster able to change appearance from human to wolf

Erinyes, Eumenides, Fury - (classical mythology) the hideous snake-haired monsters (usually three in number) who pursued unpunished criminals