Mermaids are half human and half fish.
Their tails are also their legs; in the sea, they have to clap their legs together which then attach and the scales would appear. On land they unclap them and the scales disappear and legs appear with semi-webbed feet. Mermaids' scale can vary and they are diffrent colours. They have sharp teeth and sharp nails.
Their diets are different from regular humans. While they can eat other things besides kelp and fish, they must eat meat or any kind of protein and they must also eat vegetation. Some more diabolic mermaids eat humans.
Mermaids can breathe and survive underwater no matter how deep it is. They have super strength and can used their singing to hypnotise or put a human into a trance. They also don't get cold and can swim very fast.
A mermaid's blood is special it can heal the injured. If you drink a mermaid's blood it can give you strength and can let you breathe underwater and survive underwater too. Mermaids sometimes give certain humans blood to drink so they can spend time with them underwater.