The Fairy Skriker: The Oxford English Dictionary reveals the secret, claiming that there exists a verb ‘to skrike’ which means “to utter a shrill harsh cry; to screak.” The Skriker then is the one who screaks, a “screaker.” Unlike some other members of the company from the Underworld, such as the Kelpie, which is a water-spirit or demon in Lowland Scottish folklore, or the Bogle, which is a phantom or specter of the night causing fright, the Skriker is not a traditional figure of British folklore, it is rather Churchill’s own artistic invention. The remaining creatures are taken from traditional English, Irish, and Scottish folklore.
Yallery Brown: The name of a malicious fairy in England. His appearance is extremely ugly and wrinkled, with long hair and a beard.
Black Dog: Creatures, which typically resemble black dogs though it is also often used as a generic term for canine apparitions of other colors and types.
Kelpie: In old Scotland, the Kelpie is a treacherous water devil who lurks in lakes and rivers. It usually assumes the shape of a young horse.
Green Lady: Green Ladies have power to change their forms at will. A Green Lady may sometimes deceive a traveler by appearing before him in the form of his lady-love, and, after speaking to him for a time, turn away with mocking laughter and vanish from sight. Perhaps, too, she may appear as a dog, and torment shepherds by driving their sheep hither and thither in wild confusion. Each Green Lady lives alone in a solitary place, either below a river or waterfall or in a green knoll, a forest, or a deep ravine. One is rarely seen in daytime. The Green Lady wanders about in the dusk of late evening, in the moonlight, or in darkness. She is ever a deceiver, and woe to the traveler who has not the knowledge how to overcome her spells, for she may drown him at a river ford or lead him over the edge of a precipice. It is difficult to fight against her, for if she asks a man what weapon he has, and he names it, she can, by working magic, make the weapon quite harmless.
Jennie Greenteeth: A water spirit who lurks in swamps, bogs, and slow-moving rivers. She hides in shallow, murky water with her head half-submerged like a frog and looks for unwary children to drown and devour.
The Bogle: A freakish spirit, who delights rather to perplex and frighten humankind than either to serve or seriously to hurt humans. He is like a mischievous type of Brownie. He is exactly the same as the poltergeist in his activities and habits. He is an evil-natured goblin who tortures liars and murderers. He haunts crossroads at night and likes to trick merchants. and travelers.
Brownie: The best known of the industrious domestic hobgoblins. The Brownie’s land is overall the North of England and up into the highlands of Scotland. The Brownie is small, ragged and shaggy. Some say he has a nose so small as to be hardly more than two nostrils. The most gentle of the creatures. Many Brownies can be taught to clean and do domestic chores.
Spriggan: Ghosts of giants, which haunted megaliths and standing stones, guarding the treasure buried there. They could swell to a huge grotesque shape or shrink to a small size. They were to blame for all kinds of disasters, such as falling buildings, bad weather or lost children.
Rawheadandbloodybones: A specter that frightens children. One of the evilest of the border goblins. It lives on ancient battlefields and in the ruins of fortresses, castles, and, towers. Once a cruel and violent human, its offenses against the world of Faerie condemned it to the underworld where it was first made immortal and then flayed alive. Its pain never ceases and it vents his rage against whatever human beings fall into its hands by tearing them in pieces and eating them alive.
Dr. George Popovich 