Hulder

Pen & ink and pencil on paper

A Hulder is a kind of Norwegian witch. You’ll find them haunting the deep Northern forests, hidden along paths, waiting. Not that you’d want to. They possess an ethereal beauty; with a sly smile they beckon you to follow after them. When they turn to go you’ll see their tail, but then it’s too late. Those who follow after these alluring demons are never seen or heard of again . . .

From Wikipedia: The Huldra, is a seductive forest creature found in Scandinavian folklore. (Her name derives from a root meaning "covered" or "secret".) In Norwegian folklore, she is known as the skogsrå or skogsfru/skovfrue (meaning "Lady (read, counterpart of a Lord) of the forest"). She is known as Tallemaja (pine tree Mary) in Swedish folklore, Her name suggests that she is originally the same being as the völva Huld and the German Holda. A male hulder is called a huldu, or, in Norway, a huldrekall.
Male huldes, called Huldrekall, also appear in Norwegian folklore. This being is closely related to other underground dwellers, usually called tusser. Like the female counterpart, the huldrkall is a shapeshifter who often lures girls under a fair countenance.

The huldra is a stunningly beautiful, sometimes naked woman with long hair; though from behind she is hollow like an old tree trunk, and has an animal's tail. In Norway, she has a cow's tail, and in Sweden she may have that of a cow or a fox. Further in the north of Sweden, the tail can be entirely omitted in favor of her hollow or bark-covered back.
In Norway, the huldra has often been described as a typical dairymaid, wearing the clothes of a regular farm girl, although somewhat more dazzling or prettier than most girls.