Wikipedia
The Fachen (also known as Fachan or Fachin or Peg Leg Jack 1) is a creature with only half a body in Scottish and Scots-Irish folklore. Supposedly its appearance, which includes a mane of black feathers tufted at the top and a very wide mouth, is so frightening that it induces heart attacks. It can destroy an orchard with a chain in its strong, singular, withered arm, in a single night. A story in John Francis Campbell's Popular Tales of the West Highlands features a Fachen named Nesnas Mhiccallain being defeated in a race by the story's hero, Murachadh Mac Brian, who became king of Ireland. In Popular Tales of the West Highlands the Fachen is described as follows:
Ugly was the make of the Fachin; there was one hand out of the ridge of his chest, and one tuft out of the top of his head, it were easier to take a mountain from the root than to bend that tuft.
It is also known as Direach Ghlinn Eitidh, or the Dwarf of Glen Etive.
The Fachen is Monster in My Pocket #114, and resembles a strange, feathery insectile creature. It has one leg and arm, but also seems to possess a tail.