This list of mythical creatures that begin with this letter and I am constantly gathering information from each continent, and is continually being updated.
Boobrie (Scottish)
The boobrie is a mythological shapeshifting entity inhabiting the lochs of the west coast of Scotland. It commonly adopts the appearance of a gigantic water bird resembling a cormorant or great northern diver, but it can also materialise in the form of various other mythological creatures such as a water bull.
A generally malevolent entity, the boobrie typically preys on livestock being transported on ships, but it is also fond of otters, of which it consumes a considerable number. In its manifestation as a water horse the creature is able to gallop across the top of lochs as if on solid ground. During the summer months it is seen infrequently as a large insect, sucking the blood of horses.