This mythical creature is said to have originated in the ancient Celtic folklore of Europe. It is described as a bull-like creature with a mane of flames and a tail of burning sparks. It is said to have a fierce temper and will charge
From Wikipedia
The bonnacon is a legendary creature described as a bull with inward-curving horns and a horse-like mane. Medieval bestiaries usually depict its fur as reddish-brown or black. Because its horns were useless for self-defense, the bonnacon was said to expel large amounts of caustic feces from its anus at its pursuers, burning them and thereby ensuring its escape.