Answer:
A pooka is a feared magical creature that has affinities with certain animals. According to the legends it is a shapeshifter, which means the pooka can take the shape of the animal they are particularly connected to. They get out at night and create mischief, scare the farm animals or ruin the crops.
In the role playing game Changeling: the dreaming, a Pooka is a creature inspired by the Irish mythologies, but not necessarly as mischievous. It is more of a playful spirit.
It is also something in Pokemon.