1) CERBERUS: a gigantic three-headed hound guarding the gates of Hades (the underworld abode of the souls of the dead). Cerberus had the form of a dog with three heads and a tail that ended in a dragon head. It was the offspring of Echidna, a hybrid half-woman and half-serpent, and Typhon, a gigantic monster even the Greek gods feared. In most works of art, the three heads each respectively see and represent the past, the present and the future, while other sources suggest the heads represent birth, youth and old age. Each of Cerberus' heads is said to have an appetite only for live meat and thus allow only the spirits of the dead to freely enter the underworld, but allow none to leave.
2) CHARYBDIS : a sea monster, later rationalised as a whirlpool and considered a shipping hazard in the Strait of Messina, between Italy and Sicily. Charybdis was believed to live under a small rock on one side of a narrow channel. Three times a day, Charybdis swallowed a huge amount of water, before belching it back out again, creating large whirlpools capable of dragging a ship underwater. A later myth makes Charybdis the daughter of Poseidon and Gaia and living as a loyal servant to Poseidon. She aided him in his feud with Zeus, and as such, helped him engulf lands and islands in water. Zeus, angry for the land she stole from him, cursed her into a hideous bladder of a monster, with flippers for arms and legs and an uncontrollable thirst for the sea.
4) GORGONS: three sisters who had wings of gold, brass hands and hair made of living, venomous snakes, as well as a horrifying visage that turned those who beheld them to stone. Two of the Gorgons were immortal, Stheno and Euryale, while their sister Medusa was not and she was slain by the demigod and hero Perseus. Daughters of primordial sea god and goddess Phorcys and Ceto, who personified the dangers of the sea. Born in the caverns beneath Mount Olympus.
Stheno, meaning forceful, was the eldest of the Gorgons, known to be the most independent and ferocious, having killed more men than both of her sisters combined. Stheno tends to be depicted as a thin gorgon monster with red snakes curling around her head instead of hair.
Euryale, meaning far-roaming, was the second eldest of the Gorgons. Euryale is noted for her bellowing cries, in many stories, particularly in the tale of Medusa's death at Perseus' hands.
Medusa, meaning guardian / protectress, was a ravishingly beautiful maiden, but because Poseidon had raped her in Athena's temple, the enraged Athena transformed Medusa's beautiful hair to serpents and made her face so terrible to behold that the mere sight of it would turn onlookers to stone. Medusa was beheaded by the hero Perseus who thereafter used her head as a weapon until he gave it to the goddess Athena to place on her shield.
5) GRAEAE: meaning old women or grey witches, were three sisters who shared one eye and one tooth, which they took turns using. Daughters of the sea deities Phorcys and Ceto, sisters to the Gorgons. Their names were Deino, Enyo, and Pemphredo.
Deino, meaning dread, the dreadful anticipation of horror.
Enyo, meaning horror, the waster of cities.
Pemphredo, meaning alarm.
Perseus forced them to tell the whereabouts of the three objects needed to kill Medusa (in other versions, the whereabouts of Medusa herself) by stealing their eye while they were passing it amongst themselves and ransoming it for the information. They told him to go to the Nymphs of North for that and then he threw their eye in a river so that they couldn't notify the Nymphs.
6) HARPIES: were female monsters in the form of a bird with a human face. They stole food from their victims while they were eating and carried evildoers (especially those who had killed their family) to the Erinyes. Their name means "snatchers". Daughters of Thaumas and Electra. In another version, they were agents of punishment who abducted people and tortured them on their way to Tartarus. They were vicious, cruel and violent. They lived on the islands of the Strophades. They were usually seen as the personifications of the destructive nature of wind.
The Harpies in this tradition, now thought of as three sisters instead of the original two, Hesiod's two Harpies are named Aello (strong swift) and Ocypete (the swift wing), Virgil's added Celaeno (the dark) as a third. Homer knew of a Harpy name Podarge (fleet-foot). Other names are mentioned besides those, such as: Aellopus, Nicothoe, Ocythoe, Ocypus, and more.
8) MORMO: a vampire that bit children. It is said that Mormo was used by the Ancient Greeks as a way to scare the naughty children, a kind of Boogyman, saying that he will bite their legs and leave them limp.
9) TARAXIPPUS: meaning horse disturber, was a presence blamed for frightening horses at hippodromes throughout Greece. In Greek mythology, they were thought to reside in the bends of the hippodromes, right where the vehicles were turning. It was believed that they appeared suddenly -invisible to the rider- and terrified the horses, causing the vehicle to crash and the death of the contestants.
10) LAMIA: the queen of Lybia who became a demon. In the form of a ghost, she grabbed and devoured children. Aristophanes claimed that her name derived from the Greek word "laimos" (gullet), referring to her habit of devouring children.
Daughter of Poseidon and Lybia. In the myth, Lamia was a mistress of the god Zeus, causing Hera's jealousy, who then killed all of Lamia's children and transformed her into a monster that hunts and devours the children of others. Another version had Hera merely stealing away all of Lamia's children and it being Lamia herself, losing her mind from grief and despair, who started stealing and devouring others' children out of envy, the repeated monstrosity of which transformed her into a monster on its own.
In later stories, Lamia was cursed by Hera with the inability to close her eyes so that she would always obsess over the image of her dead children. Zeus then gave her the ability to remove her eyes and thus be able to rest.