Púca

The púca (Irish for spirit/ghost; plural púcaí), pooka, phouka is primarily a creature of Celtic folklore. Considered to be bringers both of good and bad fortune, they could help or hinder rural and marine communities. Púcaí can have dark or white fur or hair. The creatures were said to be shape-changers, which could take the appearance of horses, goats, cats, dogs, and hares. They may also take a human form, which includes various animal features, such as ears or a tail.

Phouka can come to be in 4 different ways I know of. One way is simply to have Phouka parents. Another is for a fae spirit to be born to an animal, or for a spirit to be taken from an animal and replaced with a fae one. It is also possible for an animal to wander into the Faerie realm the same way humans sometimes do. Once there, some circumstance, even long enough exposure, could give them fae nature, thus them becoming Phouka.