When human girls turned mermaids/born mermaids who have acquired legs came in contact with water for ten seconds, they will grow long copper colored scaly tails and a matching scaly top. The tails are covered in scales and end in a classic dolphin-shaped fluke. They also have a short dorsal fin running along the backs of their tails from their waists to a little more than halfway down the tail. Born mermaids are also ignorant to the human world, of course.
When human boys turned mermen/born mermen who have acquired legs came in contact with water for ten seconds, they will grow long light blue colored tails. The tails are covered in scales and end in a fluke that, unlike a mermaid's, doesn't look like a dolphin's, instead have pointy tips. They also have a short dorsal fin running along the backs of their tails from their waists to a little more than halfway down the tail. Mermen haven't been seen for years since they've been hiding on land (More on that later)and have an easier time adjusting to human life.
When a human turns into a mermaid their clothes seem to disappear and once dry the clothes reappear. Born merpeople do not have legs, they must use a spell to acquire legs. Once they do acquire legs they will need some time to get used to walking. Also once they transform for the first time they will not have clothes since they didn't have them in the first place. The magic used for this spell can only come from the moon itself, a moon ring, the Trident or any other object that captures moonlight.
Mermen are considered power-hungry by the mermaids, and would do anything to obtain more power. Because of this a war between a pod of mermen and a mermaid from all five oceans started after the merman pod gained control over the trident which gave them power over land and sea in which they used destructively. The mermaids won the war and hid the trident in Mako Island. After the war mermen moved to live on land and no longer live in pods.
A pod is a group of mermaids/mermen. In every pod mermaids have for finish mermaid school before being granted a moon ring. Mermaid school teaches the mermaids how to use their powers for their daily life, to protect their pod, Mako Island and the moon pool. The mermaids harness the powers of the moon through their moon rings which can only be earned after showing maturity, responsibility, braveness and loyalty towards the pod. They also have the ability to cast spells and enchantments by singing and create a wide variety of potions using ingredients from the sea.
During a full moon turned mermaids/mermen tend to act strangely until the night is over. Also they tend to be pulled towards Mako Island.
Despite what you may think Merpeople love sea food. Once a human becomes a mermaid they will have craving of sea food even if they didn't like it before
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Source:
http://makomermaids.wikia.com/wiki/MerpeopleIf you would like to read more^