This list of mythical creatures that begin with this letter and I am constantly gathering information from each continent, and is continually being updated.
Ouroboros (Worldwide)
The ouroboros or uroboros is an ancient symbol depicting a serpent or dragon eating its own tail. The ouroboros entered Western tradition via ancient Egyptian iconography and the Greek magical tradition. It was adopted as a symbol in Gnosticism and Hermeticism and most notably in alchemy. Some snakes, such as rat snakes, have been known to consume themselves.
In Norse mythology, the ouroboros appears as the serpent Jormungandr, one of the three children of Loki and Angrboda, which grew so large that it could encircle the world and grasp its tail in its teeth. One of the earliest known ouroboros motifs is found in the Enigmatic Book of the Netherworld, an ancient Egyptian funerary text in KV62, the tomb of Tutankhamun, in the 14th century BCE.