This list of mythical creatures that begin with this letter and I am constantly gathering information from each continent, and is continually being updated.
Oread (Greek)
In Greek mythology, an Oread is a mountain nymph. Oreads differ from each other according to their dwelling: the Idaeae were from Mount Ida, Peliades from Mount Pelion, etc. Myths associated the Oreads with Artemis, since the goddess, when she went out hunting, preferred mountains and rocky precipices.
The Oreads, like all nymphs, were envisioned as beautiful young female divinities. They inhabited and personified the mountains and were often imagined in the company of other nature gods, such as Pan or Artemis. They may have also presided over the various activities that took place in the mountains, including herding, hunting, beekeeping, tree cutting, and quarrying.