This list of mythical creatures that begin with this letter and I am constantly gathering information from each continent, and is continually being updated.
Rephaite (Jewish)
The Rephaites were a race of demi-giants found in the Old Testament, thus are considered a part of Biblical lore among most of the main branches of Christianity, Judaism and Islam; they were among the "smallest" of the giants depicted in the tales, who were believed to have regularly warred with the early Hebrew people, with other giant-like races including the Anakim and Nephilim.
In the book of Joshua, and also Deut. 3:11, which implies that Og, the King of Bashan, was one of the last survivors of the Rephaim, and that his bed was 9 cubits long in ordinary cubits. (An ordinary cubit is the length of a man's forearm according to the New American Standard Bible, or approx. 18 inches, which differs from a royal cubit. This makes the bed over 13 feet long.