They could sit on rocks just offshore luring stupid guys to their doom. They look really hot, but they are cannibalistic monsters.
The animations would be of the girls combing their hair and the sound would be wordless singing, "La la la."
at night they could grow legs, toss on a slinky dress and go on land, "Hey sailor!" Roawrrrrr! chomp! gulp!
there could be packs of mermaids hunting the docks at night. a real ladies night out. a few drinks, a bite to eat...
this could work. yeah. it would be scary. for the married guys at least.