A Thestral is a breed of winged horses with skeletal body, face with reptilian features, and leathery wide wings that resembles a bat.
They are very rare, and are considered dangerous by the Ministry of Magic. Thestrals are, undeservedly, known as omens of misfortune and aggression by many wizards because they are visible only to those who have witnessed death.
Author of the customized Little Pony: Woosie in Deviant Art
