This list of mythical creatures that begin with this letter and I am constantly gathering information from each continent, and is continually being updated.
Changeling (European)
A changeling, also historically referred to as an auf or oaf, is a human-like creature found throughout much of Euro-Asian folklore. A changeling was a substitute left by a supernatural being on kidnapping a human being. Often the changeling was a supernatural being made magically to look like the kidnapped human.
Usually, the kidnapped human was a child; but there were cases, particularly in Scandinavia and Ireland where adults were taken. In Irish legend, a fairy child may appear sickly and will not grow in size like a normal child, and may have notable physical characteristics such as a beard or long teeth. They may also display intelligence far beyond their apparent years and possess uncanny insight.