Amalthean Goat - The Amalthean goat is said to have been the nurse of Zeus in Greek mythology. It's mentioned in The Chimera's Curse when it's discovered that a chimera is roaming Merlin's Wood. Connie's little brother, Simon, is a companion to the Amalthean goat, the Nemean lion, and the great snake, and all three are brought to him before he goes to face the chimera.

Banshee - Banshees are creatures that, in Gaelic mythology, wail when someone is about to die. A banshee looks like an old hag with seeweed hair, and rotted teeth, and no eyes. Connie's aunt, Evelyn Lionheart, is Companion to banshees, and she goes to revels with them often.

Cerberus - A three-headed dog from Greek mythology. In tradition, there was only one, and it guarded the gate to hell.

Chimera - A chimera has the body of a lion, the legs and hooves of a goat, and the tail of a snake's body. A chimera made its debut in The Chimera's Curse; it attacks Connie, prompting Aneena and Jane to become suspicious (and almost discover the truth about mythological creatures). Simon Lionheart turns out to be a companion to the Nemean lion and Almathean goat, two of the creatures that make up a chimera, and he calms the creature down. Because of the trio natures it possesses, a chimera is a tortured creature - its lion and snake natures are bloodthirsty and savage, while its goat nature yearns to turn and run from blood and gore and is abhorred by its counterparts' carnivorous diet.

Dragon - A traditional dragon. Dragons rescue Connie from Kullervo after Gard senses that she's in danger. Morjik is Companion to Kinga Potowska, a Trustee, and Connie and Morjik talk often. Dr. Brock is Companion to Argot. Dream-sharing between a human and dragon is a rare treat; as Dr. Brock described and he and Connie experienced, they consist of nonsensical explosion of color, light, and emotion. Connie's special Companion is a dragonet named Argand; she's fun-loving and has a golden hide, making her impervious to fire and extreme heat.

Fire Imp - An imp that dances in the heart of a fire. Fire imps are fun-loving and wild but can quickly turn deadly, for Companions that dance with them can be burned to death. Companions include Liam.

Frost Wolf - A frost wolf is a great wolf that travels through shadows; it's fictional, in that they were creatively and brilliantly created by Julia Golding. Frost wolves were explored in Mines of the Minotaur. Col's friend Rat is a Companion to them, specifically Fenris. Frost wolves' breaths are deadly cold; one breath causes coldness is, a second causes sleep, and third causes frost bite They're fun-loving and freezing to the touch.

Gorgon - such as Medusa. A gorgon is a beautiful creature (which Col before thought they were ugly until meeting his Mother's Gorgon) - a woman who incubates a snake's brood, which then hatch and live on her head. Looking into a gorgon's eyes turns one to stone (petrification.) Col's mother, Cassandra Lang, is Companion to one, and she causes Col to meet her Companion; Col is then brought to Kullervo, possessed by him, and trained until Col is rescued.

Great Eagle - A member of the species of the Great Eagles, the ancestors of modern-day eagles. They're huge and nest as far away from humans as possible - they may be dying out. They're cunning but mercurial.

Great Snakes - A member of the species of the Great Snakes, the ancestors of modern-day snakes. Nothing is known of them. Simon Lionheart meets one along with an Amalthean goat and a Nemean lion before he faces the chimera in Chimera's Curse; he's Companion to all three.

Hydra - a nine-headed creature that lives in the sea. When one of its heads is decapacitated, two grow back to replace it.

Kelpie - a water horse that lives near swamps, often seen with seaweed tangled in its mane. It acts friendly and kind around humans, but once mounted, it secretes an adhesive that anchors the victim to its back, then plunges into the swamp, drowning the victim. Will-o'-the-wisps practice the same dark tricks and are found in the same swamps as kelpies are.

Kraken - an immense creature with many tentacles that live in the deepest parts of the sea. They're cold and distant; no one knows anything about them because they're almost never seen. Mack Clamworthy, Col's dad, is companion to one.

Kullervo - there's only one of him! He's an evil shapeshifter, the antagonist of the story, and special Companion to Connie (and all Universals).

Minotaur - a creature from Greek mythology with a bull's head and legs and a man's body and arms. It stands upright. A minotaur meets Connie in Mines of the Minotaur and befriends her, giving her advice and aiding her later in the story.

Moyang Melur - only referred to in the series. In a speech at a grand meeting, it's used as an example of an endangered species, The moyang melur is a half-tiger, half-man creature that in Malay culture stole a bag containing the rules of culture, then escaped to the moon with them.

Nemean Lion - same deal as with the Amalthean goat. Simon Lionheart is a companion to the Nemean lion, Amalthean goat, and great snake. The Nemean lion was a vicious beast with impenetrable golden fur; its claws were sharper than swords and could cut through armor.

Pegasus - a winged horse; good-natured and peace-loving. Col and his mentor are Companions of pegasi.

Phoenix - a majestic, proud bird that is made of fire; its back burns everything and everyone but those who it trusts and loves, such as its Companion.

Rock Dwarf - a traditional dwarf with craggy mineral features. They can sense a great deal of things by being in contact with the earth; Gard sensed that Kullervo had Connie because Connie was touching ground. Rock dwarves are very wise. Gard's Companion, Frederick Cony, passes away, and Gard tells Connie that long life (rock dwarves live for very long) can be sad, hard, and long, and he advises her.

Selkie - a creature that transforms into a human on land and a seal in water. Selkies need to return to the water every now and then; in traditional mythology, it was said that selkies were humans with seal skins, and when the skins were stolen, they were powerless (this doesn't hold true in the series). All selkies in mythology were female, but Col and Connie's friend, Jessica Moss, is a Companion to a protective male selkie named Arran, and the two are seen checking the waters around the oil company in Secret of the Sirens.

Siren - a gorgeous creature with great wings, a melodic voice, and a hypnotic singing voice. In Greek mythology, they lured many, many men to their deaths by singing from the rocks out at sea; the men would jump into the water, trying to reach the sirens, and drown. In Secret of the Sirens, the sirens that live in the caves out at sea do the same, only to the men who work for the oil company; they're behind the mysterious deaths that make the news and stir up trouble. Connie first discovers her gift when she hides in one of the boats that Evelyn and her Companion friends take out to try and calm the sirens; Connie entreats the sirens to stop the murders, and they eventually do. Sirens are Connie's first mythological encounter.

Stone Sprite - cold, soulless creatures made of stone. When Connie is with Colin at the base of the tree in Merlin's Wood during Chimera's Curse, stone sprites approach them from out of the ground and try to petrify Connie and Colin.

Storm Bird - aka thunderbird. A storm bird is a huge, fierce, and powerful bird from Native American mythology that brings strong winds, rain, dark clouds, and lightning (storms - dun dun dun). Thunder follows its wingbeats, and wherever it flies lightning erupts.

Storm Giant - A storm giant is an immense being made of the weather elements that brings storms. Its legs are seen as two giant pillars of clouds. Companions often sit on their shoulders high up in the clouds. Storm giants carry lightning bolts in pouches by their waists and can fire them with accuracy. Col went up with Skylark against one (Hoo and Shirley Masterson, while Ivor Coddrington, Hoo's Companion and Shirley's mentor, advised the two on the ground).

Sylph - An invisible being of the air, usually a woman. A sylph assures Connie that she will usher the soul of a newly dead old man to heaven when Connie is about to take on Kullervo.

Unicorn - a horse with a long spiral horn that stems from its forehead. It has cloven hooves and is usually a solid gold, silver, or white. It can purify waters, heal, and provide emotional peace to those in its presence. Though they were portrayed by very early mythology to be fierce and savage, later mythology presented them as traditionally peaceful and mellow creatures, and they are. Windfoal, a unicorn, is Companion to Kira Okona, a Trustee; Connie meets with them in the fourth book.

Water Sprite - Found in springs and fresh water sources. Water sprites kind and caring and good listeners. Col's grandmother, Lavinia Clamworthy, is a water sprite Companion; her companion is Issoon.

Will-o'-the-wisp - mentioned in the same meeting that the moyang melur are. No one knows what exactly they are, only mysterious lights that lead unsuspecting victims into swamps to drown. Apparently, they're living creatures. They're found in swamps, just like kelpies are.

Wood Sprite - a small creature with knobby, woody exteriors, leafy extensions, and beady dark eyes. It lives in trees, and Connie saw one when she was up the tree in Merlin's Wood. Rat, Col's friend, also sees wood sprites, and he mentions this to Col.