This list of mythical creatures that begin with this letter and I am constantly gathering information from each continent, and is continually being updated.
Yong (Korean)
Korean folk mythology states that most dragons were originally imugis, or lesser dragons, which were said to resemble gigantic serpents. There are a few different versions of Korean folklore that describe both what imugis are and how they aspire to become full-fledged dragons. Koreans thought that an imugi could become a true dragon, or yong or mireu, if it caught a Yeouiju which had fallen from heaven.
Another explanation states they are hornless creatures resembling dragons who have been cursed and thus were unable to become dragons. By other accounts, an imugi is a proto-dragon that must survive one thousand years in order to become a fully-fledged dragon. In either case, they are said to be large, benevolent, python-like creatures that live in water or caves, and their sighting is associated with good luck.