Cerberus is a well known creature in ancient mythology. Hades’ loyal guard dog, Cerberus was a massive hound with three heads that guarded the entrance to the underworld. It was said that the beast only had an appetite for living flesh and so would only allow deceased spirits to pass, while consuming any living mortal who was foolish enough to come near him. It is said that the three heads were meant to symbolize the past, present and future.

Cerberus is probably best known as the twelfth and final labor that Heracles performs.
Heracles must enter the underworld, wrestle the beast using no weapons, and then bring Cerberus to the surface world, alive, to present to the Mycenaean king Eurystheus. Heracles tackled the beast; then using his great strength, throws the animal over his shoulder and drags him to the mortal world. Upon seeing Cerberus, Eurystheus was so terrified that he hid in a large vase and begged Heracles to return the hell hound back to Hades.
The domain of Hades in Greek mythology was not only hell, but was the whole of the afterlife. The realm was Tartarus (hell), the Asphodel Meadows (nothingness), and the Elysian Fields (paradise).
Agostino Carracci (1557–1602)
The Crocotta
The crocotta is a mythical dog-wolf of India or Ethiopia, linked to the hyena and said to be a deadly enemy of men and dogs. Pliny variously described the crocotta as a combination between dog and wolf or between hyena and lion.

"its eyes have a thousand variations of color; moreover that when its shadow falls on dogs they are struck dumb; and that it has certain magic arts by which it causes every animal at which it gazes three times to stand rooted to the spot."
"In Ethiopia there is an animal called crocottas, vulgarly kynolykos [dog-wolf], of amazing strength. It is said to imitate the human voice, to call men by name at night, and to devour those who approach it. It is as brave as a lion, as swift as a horse, and as strong as a bull. It cannot be overcome by any weapon of steel."
The Basilisk
In European legends, a basilisk is a legendary reptile said to be king of the serpents and to have the power to cause death with a glance. According to Pliny the Elder, the basilisk of Cyrene leaves a wide trail of deadly venom in its wake, and its gaze is likewise lethal; its only weakness is the odor of the weasel.

The legend of the basilisk and its association with the weasel in Europe may be inspired by accounts of Asiatic snakes (such as the king cobra) and their natural predator, the mongoose.
Stories gradually added to the basilisk's deadly capabilities, such as describing it as a larger beast, capable of breathing fire and killing with the sound of its voice.

Some even claimed it could kill not only by touch, but also by touching something that is touching the victim, like a sword held in the hand. Some stories even claim its breath to be highly toxic and will cause horrible death.
In late Greek mythology ichthyocentaurs were a race of centaurine sea-gods with the upper body of a human, the lower front of a horse, the tail of a fish, and lobster-claw horns on their heads. The best-known members of this race were Aphros and Bythos, two half-brothers of the wise centaur Chiron. The sea-centaurs were probably derived from the divine fish of Syrian mythology.

Ichthyocentaurs upper bodies took the form of a human torso down to the hips, and the lower that of a fish, with two horse legs protruding from this intersection.

Bythos and Aphros
Some ichthyocentaurs wore crowns while others were depicted with horns often resembling crustacean claws. These two sea-gods, though little remembered, were set in the sky as the astronomical constellation Pisces.
A hellhound is a supernatural dog in folklore. A wide variety of hellish supernatural dogs occur in mythologies around the world. Some European legends state that if someone stares into a hellhound's eyes twice or more, that person will surely die.

Hellhounds often have fire-based abilities and appearance. They are often assigned to guard the entrances to the world of the dead, such as graveyards and burial grounds, or undertake other duties related to the afterlife, such as hunting lost souls. In European legends, seeing a hellhound or hearing it howl is an omen or even a cause of death. They are said to be the protectors of the supernatural.
In Greek mythology the hellhound belonged to Hades, the Greek god of death and the underworld. It's name in Greek mythology is Cerberus. It has three heads and guards the gates of hell.

The Bearer of Death is a term often used in describing the Hellhound. Hellhounds are said to be as black as coal with a smell of burning brimstone. They leave behind a burned area wherever they go.

Hades with Cerberus - Pluto Carricci painting
Hellhounds of myth is common across Great Britain and Western Europe.

In southern Mexico and Central America folklore, the Cadejo haunts travelers who walk late at night.
The Valkyries: Chooser of the Slain
In Norse Mythology Valkyries are female warlike virgins, who are mounted on horses and armed with helmets and spears. They decide who will die in battle. They hover over the battlefield like birds of prey.

In ancient Norse mythology, before they were linked to Odin and Ragnarok, the Valkyries were sometimes represented in carvings as carrion-eating ravens. The original Valkyries, appearing on battlefields as soon as the fighting was over, would weave tapestries from the intestines of slain warriors and feed corpses to their pet wolves.
Between the 3rd and 11th centuries, the perception of the Valkyries changed and they became associated with Odin. On the battlefield the Valkyries chose the souls of the bravest slain warriors to become Einherjar, soldiers to fight for Odin at Ragnarok, the final battle between the gods and the giants. Half of those who die in battle would go to Valhalla. The other half will go to the goddess Freya’s afterlife field Folkvangr. Freya always has the first pick, of the fallen Vikings. Odin allows some of the maidens to take the form of beautiful white swans, but if a Valkyrie is seen by a human without her swanlike disguise, she will become an ordinary mortal and can never return to Valhalla.
Once in Valhalla the dead warriors became Einherjar. (Old Norse "single fighters") Inside Valhalla the Valkyries changed clothes. Wearing simple white robes, they served the Einherjar fine foods, such as wild boar, and sacred wine made from honey. They would remain the Einherjar's servants until Ragnarok.
Valkyries were Odin's bodyguards and messengers. Mortals saw their flickering armor and light streaming from their spears. In the Middle Ages Scandinavians believed the northern lights (aurora borealis) were the Valkyries flying across the night sky. Valkyries usually appeared in groups of nine.

The Ride of the Valkyries is the popular term for the beginning of Act III of Die Walküre, by Richard Wagner. The main theme of the ride was first written down by the composer on 23 July 1851. It is one of Wagner's best-known pieces.

In Greek mythology, a Gorgon is a female creature. The name derives from the ancient Greek word gorgós, which means "dreadful". The term commonly refers to any of three sisters who had hair made of living, venomous snakes. They turned those who beheld them to stone. Traditionally, while two of the Gorgons were immortal, Stheno and Euryale, their sister Medusa was not, and she was slain by Perseus.

Gorgons were a popular image in Greek mythology, images of the Gorgons were put upon objects and buildings for protection.
The concept of the Gorgon is at least as old in classical Greek mythology as Perseus and Zeus. One of the earliest representations is on an electrum stater from Parium. Other early eighth-century examples were found at Tiryns. Going even further back, there is a similar image from the Knossos palace, dating to the fifteenth century BC.
Typhon was a monstrous giant and the most deadly creature in Greek mythology. Typhon was the last son of Gaia, and was fathered by Tartarus. Typhon and his mate Echidna were the progenitors of many famous monsters.

Hera, angry at Zeus for having given birth to Athena by himself, prayed to Gaia to give her a son as strong as Zeus, then slapped the ground and became pregnant. Hera gave the infant Typhon to the serpent Python to raise, and Typhon grew to become a bane to all mortals.
According to Hesiod, Typhon was "terrible, outrageous and lawless", and on his shoulders were one hundred snake heads, that emitted fire and every kind of noise. "Strength was with his hands in all that he did and the feet of the strong god were untiring. From his shoulders grew a hundred heads of a snake, a fearful dragon, with dark, flickering tongues, and from under the brows of his eyes in his marvellous heads flashed fire, and fire burned from his heads as he glared."

Typhon "was joined in love" to Echidna, a monstrous half-woman and half-snake, who bore Typhon "fierce offspring"
Typhon challenged Zeus for rule of the cosmos. Angered, Zeus used his thunderbolt to easily overcome Typhon, who was cast down into Tartarus.

Most accounts have the defeated Typhon buried under either Mount Etna in Sicily, or the volcanic island of Ischia, the largest of the Phlegraean Islands off the coast of Naples, with Typhon being the cause of volcanic eruptions and earthquakes.
In Greek and Roman mythology, a harpy was a half-human and half-bird personification of storm winds. Their name means "snatchers" or "swift robbers". They were generally depicted as birds with the heads of maidens, faces pale with hunger and long claws on their hands. Roman and Byzantine writers detailed their ugliness. Pottery art depicting the harpies featured beautiful women with wings. They are described as human-vultures.
The most celebrated story in which the Harpies play a part is that of King Phineus of Thrace, who was given the gift of prophecy by Zeus. Angry that Phineus gave away the god's secret plan, Zeus punished him by blinding him and putting him on an island with a buffet of food which he could never eat because the harpies always arrived to steal the food out of his hands.

Harpies remained vivid into the Middle Ages. In Dante's Inferno, the tortured woodland was infested with harpies, where the suicides have their punishment in the seventh ring of Hell.
The Edimmu
The edimmu were envisioned in Sumerian religion as the ghosts of those who were not buried properly. They were considered vengeful toward the living and might possess people if they did not respect certain taboos. They were thought to cause disease in the living. The edimmu were also thought to be "wind" spirits that sucked the life out of the susceptible and the sleeping.
An ekimmu is an angry undead spirit that hates humans, demihumans and humanoids, and seeks vengeance against the living.
The Chimera

The Chimera of Arezzo, bronze, Etruscan, 5th century BC
In Greek mythology the Chimera was a monstrous fire-breathing hybrid, composed of the parts of more than one animal. It is usually depicted as a lion, with the head of a goat arising from its back, and a tail that ended with a snake's head. It was thought to be one of the terrifying offspring of Typhon and Echidna and a sibling of such monsters as Cerberus and the Lernaean Hydra.

The sighting of a Chimera was a certain omen for disaster. Homer's description in the Iliad: "a thing of immortal make, not human, lion-fronted and snake behind, a goat in the middle, and snorting out the breath of the terrible flame of bright fire."
The Chimera was defeated by Bellerophon with the help of Pegasus, at the command of King Iobates of Lycia. Since Pegasus could fly, Bellerophon shot the Chimera from the air in safety. Bellerophon finished the Chimera off by equipping his spear with a lump of lead that melted when exposed to the Chimera's fiery breath.
Four Horsemen of the Apocalypse
The Four Horsemen of the Apocalypse are described in the last book of the New Testament of the Bible, called the Book of Revelation of Jesus Christ to John of Patmos, at 6:1-8. The chapter tells of a book or scroll in God's right hand that is sealed with seven seals. The Lamb of God opens the first four of the seven seals, which summons four beings that ride out on white, red, black, and pale horses.

The four riders are often seen as symbolizing Pestilence, War, Famine, and Death. The Christian apocalyptic vision is that the four horsemen are to set a divine apocalypse upon the world as harbingers of the Last Judgment.

Albrecht Dürer, Knight, Death and the Devil, 1513
The first horseman is called Pestilence, and is associated with infectious disease and plague. It appears at least as early as 1906. "They were given power over a fourth of the earth to kill by sword, famine, plague, and by the wild beasts of the earth." (Revelation 6:7-8 NASB). It is a matter of debate as to whether this passage refers to the fourth rider, or to the four riders as a whole.

The rider of the second horse is often taken to represent War. His horse's color is red. The color red, as well as the rider's possession of a great sword, suggests blood that is to be spilled.

When He broke the second seal, I heard the second living creature saying, “Come.” And another, a red horse, went out; and to him who sat on it, it was granted to take peace from the earth, and that men would slay one another; and a great sword was given to him. — Revelation 6:3-4

When He broke the third seal, I heard the third living creature saying, “Come.” I looked, and behold, a black horse; and he who sat on it had a pair of scales in his hand. And I heard something like a voice in the center of the four living creatures saying, “A quart of wheat for a denarius, and three quarts of barley for a denarius; but do not damage the oil and the wine.”
The third horseman rides a black horse and is popularly understood to be Famine as the horseman carries a pair of balances or weighing scales, indicating the way that bread would have been weighed during a famine. — Revelation 6:5-6
The fourth and final horseman is named Death. Of all the riders, he is the only one to whom the text explicitly gives a name. Unlike the other three, he is not described carrying a weapon or other object, instead he is followed by Hades. Illustrations commonly depict him carrying a scythe.

When the Lamb broke the fourth seal, I heard the voice of the fourth living creature saying, “Come.” I looked, and behold, an ashen horse; and he who sat on it had the name Death; and Hades was following with him. Authority was given to them over a fourth of the earth, to kill with sword and with famine and with pestilence and by the wild beasts of the earth. — Revelation 6:7-8