The Deadly Little Mermaid ( 1970 )

Construction on a luxury beach resort unearths ancient bones and pirate relics. A group of frat guys partying on the beach disturb a sunken grave with their drunken antics. That night, one of them vanishes. Then another. A ghostly mermaid with barnacle-covered skin, torn fins, and broken jewelry begins stalking them from the ocean, luring them with singing before killing them in brutal, symbolic ways-slashing, drowning, dismemberment.