Troll Maiden, a Lady of the forest. Also knows as a Hulder (a seductive forest creature found in Scandinavian folklore) or Skogsfru (Norwegian folklore).
A hulder is a stunningly beautiful naked woman with long hair and an animal's tail. She is said to be a dangerous seductress who lives in the forest. The young and beautiful Huldra is moody and dangerous, but when she becomes old and ugly, she also becomes gentle and caring. A Skogsfru is said to be a deeply attractive woman that has either a hollow back or a tree stump on her back.
They are said to be generally kind but are also known to be malicious.