Familiars

A Familiar is the supposed guardian or companion of a witch or devil-worshipper that has become a common theme in fiction, though belief in them goes back to folklore.

A Familiar was envisioned as an adept shape-shifter and often had knowledge of the occult and magic, which it would share with its master or mistress - in order to keep itself hidden a Familiar would take on the form of various small animals such as frogs, toads or (most famously) black cats.

A Familiar's true form could be a Devil, a fairy/goblin or an imp - alternatively a Familiar may actually be seen as an intelligent animal-spirit (perhaps a throwback to totem-spirits of old).

Although heavily persecuted during the witch-hunt eras of history a Familiar is not necessarily an evil being in itself, as with most magic the power of a Familiar is only really evil when abused by malicious sorcerers (such as warlocks, necromancers and the stereotypical "wicked witch")