Familiars are spirits who assist witches and other sorcerers, either by being conjured or mutual agreement. Depending on who they serve, they’re considered demons, fairies, or other spirits. They appear ordinary, usually manifesting as animals, and sometimes humans.
fairies
The Pooka or Puca or Pwca is a shape-shifting creature from Celtic foklore that can change into a horse, goat, cat, dog, or hare. If they take human form, they’ll have an animal feature like ears or a tail. Pookas are tricksters and can bring good or bad fortune. The character of Puck in Shakespeare’s A Midsummer Night’s Dream was based on this creature. Image: British Goblins, W Sikes, 1881
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In Irish folklore, a changeling is a fairy child that was left in place of a human child stolen by the fae. Changelings often appear exactly like a human children but with strange differences such as long teeth, a full beard, uncanny intelligence and odd behavior. Jinn from Arabic folklore are also known to steal human children and replace them with changelings. Image: Titania and the Changeling Child (detail) by John Anster Fitzgerald, 1832-1906