Nixies

   From Norse folklore, these beings live in beautiful palaces, in bodies of fresh water. They can assume various forms, or become invisible. They resemble mermaids and mermen, but will go to market disguised as old women, or dances as young and attractive people. They are usually unfriendly, and lure people into deep water where they drowned them. They must have at least one victim a year, and used to be offered human sacrifices. Sometimes, however they would take a human mate and have children.