The Glaistig; water faerie

The Glaistig is part alluring woman and part goat, she hides her cloven hoofs under long flowing gowns and uses her good look to entice men to dance with her. Once exhausted she feeds upon their blood. But on a gentler note she is kind to children and animals ( it's obviously just men that she has a problem with!)
On the island of Iona, women leave offerings near the hollow rock where she lives. Fresh milk is left on the Glaistig Stone every evening and in return for this kindness the Glaistig will guard their livestock during the night.
In Lochaber, Scotland, a Glaistig was once caught by a local smith, he refused to release her until she gave him a herd of cattle. The cattle duly appeared but the smith was not satisfied, he demanded a house be built that neither enemy or faerie could harm.
She summoned all the goblins from the surrounding countryside and they set to work building the house for the smith. It was completed in one night, the last piece was put into place just as the cock crowed. The goblins disappeared but not the glaistig as she was still a captive of the smith. She offered her hand to complete the bargain but the smith not trusting the faerie burnt it with a red hot poker. The poor glaistig ran screaming into the hills where she bled to death. The surrounding plants and ground where she fell have ever  since been stained red with her blood. 
The house that she and the goblins built still stand but the smith did not prosper after wounding the glaistig, he became sick and the house was sold to pay for the services of a local doctor.

Faeries and Folklore of the British Isles