In case Harvey being a pooka doesn't really answer your question.
The púca (Irish for spirit/ghost), pooka, phouka, phooka, phooca, puca or púka, is primarily a creature of Irish folklore.[1] Considered to be bringers both of good and bad fortune, they could either help or hinder rural and marine communities. The creatures were said to be shape changers which could take the appearance of black horses, goats and rabbits.
Púca - Wikipedia, the free encyclopedia