4. Ningyo from Japanese Folklore
There are a lot of different descriptions of the Ningyo from having a fish head and human body, to the upper body of a human and bottom of a fish to completely fish like but with a humanoid face and arms that has sharp claws.
The obvious difference it has with the mermaids we see in movies and cartoons is that the Ningyo always looks hideous and nightmarish. So they don’t try to seduce or enchant people to come near them, they rather have nothing to do with humans.
But they are magical beings that if they were ever caught by humans, they can place a curse on the human and ensure that a tsunami would come. The only reason why people want to catch a Ningyo even with knowing they could get cursed is that people believed that by eating their flesh, their life would be extended and youth would be granted.