Greek myths include many monstrous beings. Some resemble hybrids between different species, while others are of the same species but having un-natural extra heads or limbs. There are also some un-dead monsters, such as ghosts and demons.
Centaurs - a race of half-man, half-horse beings. They were usually depicted with the upper body of a man and lower body of a horse. Most famous was Chiron, the eldest and wisest of the Centaurs. He was also the ancient trainer of heroes.
Cerberus - a three-headed monstrous hound that guarded the gates of Hades. It was there to prevent anyone from escaping the underworld. Heracles captured it in his final labor and, with the consent of Hades, brought it back before Eurystheus.
Cercopes - monkey-like thieves who plagued the land of Lydia in western Anatolia. They were punished for their crime by Zeus who transformed them into pure monkeys.
Charybdis - a sea monster which swallowed large amounts of water, forming a deadly whirlpool. It was later rationalised just as whirlpool. It was encountered by Odysseus in the Odyssey and previously by Jason and the Argonauts, when they were returning back to Iolcos.
Chimera - a monstrous fire-breathing female creature, composed of the parts of a lion, a goat and a serpent. It was depicted as a lion, with the goat's head arising from its back and a tail which ended with serpent's head. It was slain by Bellerophon.
Empusa - a vampiric demoness with a single leg of bronze and a foot of a donkey. She feasted on the young men's blood and flesh, after seducing them into sleep paralysis. She was a daughter of Hecate and spirit Mormo.
Gorgons - three cursed sisters with hair full of venomous serpents. They were all cursed by Athena because of Medusa who mated with Poseidon in a temple of the goddess. Medusa was also the only one who was mortal and capable of turning men into stone with her gaze. Others were Stheno, the most murderous, having killed more victims than other sisters combined, and Euryale, the sister most known for her death-bellowing screams.
Graeae - three old women with one tooth and one eye which they had to share among them. Their names were Deino, Enyo and Pemphredo. They were encountered by Perseus when he went to ask them about the location of the Garden of Hesperides.
Harpies - winged creatures with the bodies of birds and the heads and torsos of women. Best known for stealing food from Phineus who was punished by Zeus. The event itself was encountered by Jason and the Argonauts on the way to Colchis.
Hippalectryon - a creature with the front body of a horse(head, torso, front legs) and rear body of a rooster(tail, wings, rear legs).
Hippocamp - a sea-horse like creature with a body of a horse and a tail of a fish.
Hydra - a many-headed, ancient serpent-like beast with poisonous breath and blood so virulent that even its tracks were deadly. Variously it was said that when a head was chopped off, two new heads would grow or just a new one. Heracles encountered one which guarded the underworld entrance beneath Lake Lerna.
Ichthyocentaurs - a pair of marine centaurs with upper bodies of men, lower front parts of horses and tails of fish. Also, they wore lobster-claw horns and were half-brothers of Chiron.
Ipotane - a race of half-horse, half-humans. They are usually depicted as arms and body of humans with legs, bottom and a tail of a horse, sometimes also with the ears of a horse.
Kobalos(Kobaloi) - species of mischievous, thieving gnome-dwarfs, fond of tricking or frightening mortals. They were also depicted as funny little tricksy elves. They were companions of Dionysus.
Manticore - a monstrous creature with a head of a man, a body of a lion and a tail of a scorpion. Sometimes even depicted with the wings of a bat.
Mormo - a vampiric spirit creature who bit bad children and was a companion of goddess Hecate.
Nessus - the centaur who became a ferryman at the river Euenos. He was killed by Heracles when he kidnapped his wife Deianeira. Dying Nessus told Deianeira that his blood would ensure that Heracles would be true to her forever. But instead it killed Heracles who was then taken to Mount Olympus by Zeus.
Ophiotaurus - a cow-serpentine monster, composed of parts of a bull and parts of a serpent.
Orthrus - a two-headed, serpent-tailed dog that was a brother of Cerberus and a pet of three-bodied giant Geryon. The creature was slain by Heracles along with the giant in one of his labours.
Panes - a tribe of spirit-like creatures who had heads and torsos of men, legs and tails of goats, goatish faces and goat-horns
Satyrs - the companions of Pan and Dionysus who had human upper bodies, legs and tails and ears of a goat and pug-noses. They were often depicted dancing and drinking at the parties of Dionysus. There is also a myth of satyr called Marsyas who challenged Apollo to a music contest.
Sileni - a race of elderly companions of Dionysus which were differentiated from satyrs by having the attributes of a horse rather than a goat.
Sirens - dangerous winged bird-women whose irresistible enchanted songs lured sailors to their deaths. They were encountered by Odysseus in the Odyssey and by Jason and the Argonauts on their quest.
Sphinx - a monstrous creature with the body of a lion, wings of an eagle and head of a woman. She is mythicised as treacherous and merciless. Oedipus encountered the monster when he came to Thebes.
Taraxippi - ghostly apparitions that frightened horses on race-courses of Olympia, Isthmos and Nemea. It is said that horses were shocked by no reason while on course and crashed chariots with people in it.
Telchines - skilled metal-workers in brass and iron, with heads of a dog and flippers of a seal in place of hands.