In Irish mythology, the Púca is a mischievous, shapeshifting faerie who would assume a disguise in many forms, including a horse, rabbit, goat, goblin, dog, calf, or donkey. Most commonly, the Púca is disguised as a sleek, black horse, with burning yellow eyes and an untamed, wild mane. It is among the most frightening Faeries is some parts of Ireland, and is said to scatter livestock, break fences, and cause damage to property as well as harm humans. Although It seems to have a bad reputation, If they acquire a liking to a certain human, they will often offer advice and be a generally kind faerie. The origins of the Púca is unknown, but there is some speculation that the name could have origins in Scandinavia, the name being related to “pook” or “puke” meaning “nature spirit”.
If I’m remembering correctly this is sourced from Faeries by Alan Lee and Brian Froud.