Nuckelavee is a horse-like demon from Orcadian mythology that combines equine and human elements. It has its origins in Norse mythology, and is the most horrible of all the demons of the Scottish islands. The nuckelavee's breath was thought to wilt crops and sicken livestock, and the creature was held responsible for droughts and epidemics on land despite its being predominantly a sea-dweller.
A unique and solitary creature possessing extensive evil powers, its malevolent behaviour can influence events throughout the islands. Islanders were terrified of the creature and would not speak its name without immediately saying a prayer. It was often found in the vicinity of a beach, but would never come ashore if it was raining.
No tales describe what form the nuckelavee takes when in the sea,but its appearance on land has been recounted in graphic detail. the nuckelavee has a man's torso attached to a horse's back as if it were a rider. The male torso has no legs, but its arms can reach the ground from its position on top of the equine body, the legs of which have fin like appendages. The torso has a large head, possibly as much as 3 feet (90 centimetres) in diameter, that rolls back and forth.
The monster described by a witness has two heads; the equine head has an enormous gaping mouth that exudes a smelly toxic vapour, and a single giant eye like a burning red flame. A particularly gruesome detail is that the nuckelavee has no skin; black blood courses through yellow veins, and the pale sinews and powerful muscles are visible as a pulsating mass.