Hulder

The hulders are beautiful, elf-like women who were harmful in their interactions with human men. They are commonly seen as a type of Elf, although a more sinister version.

Myths & Legends
The Huldra are seen as beautiful women who lure human men into marrying them, and when they do so they will lose the hollow back and tail. It's said that if her fiancée sees her back before marriage he will see her for she truly is - ugly - and if he refuses to marry her, she will simply kill him, yet if he goes through with the marriage she will become human but kill him anyway. There is not much for him to be rescued from.

Danish Variation
The Danish version of a Huldra is missing their hollow back and cow tail, which is due to the different forms of tales there has been told in the Danish inns and houses. There is only few placed in the Danish lore, where you can hear about the hollow back of Elves, which is often being told with the fact that they are lustful and out for the men. But as in most of the Danish lore, they were only out for dancing and sex.

A Huldra who lost their tail and hollow back would often dance a rune dance and in the mornings you would see what appeared to be a Witch Circle (Also know as A Druid Circle).

They would often live in moss affected areas, in the forest or close to swamps, with the Elven king. They were seen as pale beautiful women, wearing white dresses and having light blonde hair. They would often dance on the top of a burial mound, early in the mornings or when the mist was thick.

If a human man saw them dance, he'd be hypnotised by the dancing and join them. Often the girls would dance him to death, as time slowed when dancing with them. For the man there would only have gone a few hours, while back in the natural world years, maybe even decades would have gone by.

If one decided to kidnap a human, they'd be used for sex. those who had sex with the Elves would often become mentally insane or die. People in the Danish households often exclaimed that The more time you spent with the Elvenpeople, the worse it would get you.