Arwah Kuntilanak Duyung

Arwah Kuntilanak Duyung (Spirit of the Kuntilanak Mermaid) is a comedy-horror Indonesian film about a mermaid kuntilanak who terrorizes people. A kuntilanak is a monstrous female spirit who in some versions was previously a living human woman, who after death became the vengeful creature due to a crime that was done to her. This movie features a kuntilanak who is also a mermaid, and her rage is because she was murdered while she was pregnant. Don't mistake this for a straight-up horror movie, though! Lots of toilet humour and slapstick bumbling around various spirits (the kuntilanak isn't the only supernatural being hanging around).

Despite this film's mermaid (Dewi Perssik) being a literal monster, her mermaid form is actually pretty conventional, with a shiny golden tail. She does swim a bit but there are no underwater scenes and mostly she goes around making dolphin-ish noises to jumpscare people around the seaside village where she died. She ultimately manages to kill the man who originally killed her, and gets a happy ending of sorts because another woman is killed the same way and joins her in the ocean.