Sluagh
A horde of evil spirits, who fly in groups like birds. According to Irish legends, they are the souls of deceased sinners and they try to take other souls with them. They come flying from the west and therefore, when someone is dying, people keep the windows on the west-side closed. This way, the soul of the deceased can not be intercepted before it reaches heaven.


Styx

Styx ("hate") is the Greek goddess of the river of death in the underworld. She was usually said to be the daughter of Erebus and Nyx. She was married to Pallas by whom she had Zelus, Nike, Cratos and Bia. The gods swore their oaths by this river, for violating such an oath would result in the loss of their immortality.


Succubis

In medieval European folklore, the incubus is a male demon (or evil spirit) who visits women in their sleep to lie with them in ghostly sexual intercourse. The woman who falls victim to an incubus will not awaken, although may experience it in a dream. Should she get pregnant the child will grow inside her as any normal child, except that it will possess supernatural capabilities. Usually the child  grows into a person of evil intent or a powerful wizard. Legend has  it that the magician Merlin was the result of the union of an  incubus and a nun.
A succubus is the female variety, and she concentrates herself on men. Etymology: (Latin) incubare "to lie upon, in, with".


Tatzlwurm
In German folklore, the Tatzlwurm is a winged, fire-breathing dragon.


Dragon

Few creatures of folklore and mythology conjure up the mental images of the dragon. Also known as wurm, wyrm and firedrake, these mercurial creatures pervade almost every pantheon of classical mythology and have become an integral inclusion of an entire genre of fantasy literature.
Descriptions of the beast's benevolence vary from the playful Puff (of Peter Yarrow's song) to the sinister Smaug in J.R.R. Tolkien's "The Hobbit". Babylonian legends portray the Queen of Darkness as a multi-headed dragon - Tiamat. Walt Disney's Sleeping Beauty features a battle between Prince Phillip and the evil Maleficent and the Germanic myth "Die Neiberling" climaxes with the battle between Siegfried and the giant Fafnir, who has transformed himself into a wyrm in an effort to become more frightening.
Physical characteristics of dragons also vary but several consistencies are usually present. The beasts are typically depicted as huge lizards, larger than elephants on average. Long fangs are generally accepted as are twin horns of varying length. Western cultures generally include large bat-like wings giving the dragon the capability of flight. But eastern dragons, usually wingless, use a more magical means of flying. As well, eastern dragons tend to be more snake-like in nature, albeit with front and rear legs.
Most dragons will be covered in scales, although there are some with a leathery skin. Coloring ranges the entire gamut of the spectrum but red, green, black and gold appear to be the most common. It is also generally accepted that most dragons are magical creatures in nature and have the ability to breathe fire (as a weapon). Some dragons may have a modification in this breath weapon (frost, lightning, gas) but this appears to be purely a fabrication of fantasy role-playing games and the myths they spawn.
For those interested in a rational theory of what dragons may have been like and why there are no fossils of them, consider reading Peter Dickinson's "The Flight of Dragons" (Fitzhenry and Whiteside Ltd. 1979.) In it, Dickinson speculates that something in the dragon's physiology produced vast amounts of hydrogen gas, which would account for its ability to fly (much like a zeppelin) and the need to periodically exhale hydrogen, an inherently flammable gas that flint-like teeth could easily spark into combustion.
Obviously, a dragon could not fly with his wings only; the wings would have to be around 600 feet wide to support one. However, we DO see something flying today which has no wings. Ever heard of the Goodyear blimp? It stands to reason, then, that a creature could have some kind of chemical mechanism wherein he could "fill" himself with a lighter-than-air gas, in which point, if he was light enough (which the blimp is), he could rise to the heavens, with the wings being used for mild propulsion and steering. When he releases the gas in a kind of belch (to get back down!), a chemical in his mouth ignites the gas, creating the tell-tale breath of fire. Remember, cows make methane (a highly flammable gas) in their stomachs. These chemicals would also create the highly corrosive liquid known as "dragon's blood," which would explain its ability to melt swords and the like away. It would also corrode the dragon carcass comparatively quickly, erasing all evidence of the dragon (and thus all fossil evidence).
As for why dragons hoarded gold, you should realise that gold will not make a sharp point (for long) when laid upon, and it also could not be affected by the "dragon's blood" at all. This is most important: anywhere the dragon would lie would be a chemical swamp rather quickly; gold would allow for a lair which could stay a lair for a while. Many more aspects of dragons are covered in the book which are not covered here; if you have an interest in dragons, this is a source for straight reasoning on how they could have existed.


Tiamat


In Babylonian myths, Tiamat is a huge, bloated female dragon that personifies the saltwater ocean, the water of Chaos. She is also the primordial mother of all that exists, including the gods themselves. Her consort is Apsu, the personification of the freshwater abyss that lies beneath the Earth. From their union, saltwater with freshwater, the first pair of gods were born. They are Lachmu and Lachamu, parents of Ansar and Kisar, grandparents of Anu and Ea.
In the creation epic Enuma elish, written around 2000 BC, their descendants started to irritate Tiamat and Apsu so they decided to kill their offspring. Ea discovered their plans and he managed to kill Apsu while the latter was asleep. Tiamat flew into a rage when she learned about Apsu's death and wanted to avenge her husband. She created an army of monstrous creatures, which was to be led by her new consort Kingu, who is also her son. Eventually, Tiamat was defeated by the young god Marduk, who was born in the deep freshwater sea.
Marduk cleaved her body in half, and from the upper half he created the sky and from the lower half he made the earth. From her water came forth the clouds and her tears became the source of the Tigris and the Euphratus. Kingu also perished, and from his blood Marduk created the first humans.


Troll

In Scandinavian myth, trolls are ugly, malicious creatures and the enemies of mankind. They are much bigger and stronger than humans, and leave their caves only after dark to hunt. If they are exposed to sunlight they will instantly turn to stone. Trolls are very fond of human flesh. In later myths they are roughly the size of humans or elves, and thought to be the owners of buried treasures. They are sometimes, although very rarely, portrayed as friendly, less ugly creatures.