This list of mythical creatures that begin with this letter and I am constantly gathering information from each continent, and is continually being updated.
Bukavac (Serbia)
Bukavac (Serbo-Croatian) is a demonic mythical creature in Slavic mythology. Belief in it existed in Syrmia. Bukavac was sometimes imagined as a six-legged monster with gnarled horns and bright blue eyes. It lives in lakes and pools, coming out of the water during the night to make a loud noise (hence the name: buka – noise). It would jump onto people and animals and strangle them.
The females generally sit behind the males and tend to be black in color. They both only attack at night. I know this might creep you out but there have been accounts of animals found strangled by lakes. It has six legs and is nocturnal, he has antlers and in some cases can move freely on land, but due to his huge body (9 foot) is likely to struggle.