This list of mythical creatures that begin with this letter and I am constantly gathering information from each continent, and is continually being updated.
Bonnacon (Medieval Bestiaries)
The bonnacon (also called bonasus or bonacho) 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.
The bonnacon is most often illustrated as a beast the looks like a bull or ox, with curled horns, being attacked by men (sometimes dressed in chain mail like soldiers) with a spear or an ax. The beast is usually shown spraying its dug in defense, often with the hunters deflecting the spray with a shield.