What seductive forest spirits have cow tails?

The story behind the answer

Huldra is correct. In Scandinavian (Norse) folklore, the Huldra is a beautiful forest spirit who appears human from the front but betrays her otherworldly nature with a cow’s tail and often a hollow, bark-like back. She lures travelers and woodsmen; kindness or proper respect brings rewards and protection, while mistreatment can lead to misfortune. In some tales, a church wedding “tames” her and makes the tail disappear.

To remember: Huldra sounds like “herd,” hinting at cattle—so think cow’s tail. By contrast, the Sidhe and Banshee are Irish spirits, and Yuki-onna is a Japanese snow woman. The Huldra reflects the Viking-age respect for nature’s power: enchanting, generous to the worthy, and dangerous to the careless.