Morphology and physiology
According to legend, the púca is a deft shape shifter, capable of assuming a variety of terrifying forms. It may appear as a horse, rabbit, goat, goblin, or dog. No matter what shape the púca takes, its fur is almost always dark. It most commonly takes the form of a sleek black horse with a flowing mane and luminescent golden eyes. 
If a human is enticed onto a púca's back, it has been known to give them a wild ride. But unlike a kelpie, which will take its rider and dive into the nearest stream or lake to drown and devour him, the púca will do its rider no real harm. The púca has the power of human speech, and has been known to give advice and lead people away from harm. Though the púca enjoys confusing and often terrifying humans, it is considered to be benevolent.
They generally have green eyes. Like dragons, they have a fondness of riddles, but unlike dragons, they are very sociable. Phookas are witty and have few family members, but hundreds of friends which they enjoy getting together with. (Especially if it is to play a prank on any unsuspecting humans.)