This list of mythical creatures that begin with this letter and I am constantly gathering information from each continent, and is continually being updated.
Reptilian Humanoid (Global)
Several ancient people all over the world have described reptilian humanoids. Common in numerous mythologies are tales of reptilian creatures (usually not humanoid) who are often, but not always, hostile to human beings. Also rather common are myths of "Serpents of Wisdom" who enlightened humanity before the dawn of civilization.
In the Americas, Native American mythology refers to lizardmen in many of their myths and tales, including those of transformation into snakes. Greek mythology sometimes depicts the Titans and even the god of the northern wind as being reptilian men.