Kelpie
Kelpie, or water kelpie, is a shape-shifting water spirit inhabiting the lochs and pools of Scotland. It is a Celtic legend, and other cultures seem to have adopted it as well. It has usually been described as appearing as a horse, but is able to adopt human form. Some accounts state that the kelpie retains its hooves when appearing as a human, leading to its association with the Christian idea of Satan as alluded to by Robert Burns in his 1786 poem "Address to the Devil".