-Soop, just before sending a flood to Fairy Haven in Fairy Haven and the Quest for the Wand.
Mermaids are magical, aquatic creatures of the water with the heads, arms and torsos of beautiful women and the tails of fish. Never Mermaids live in Mermaid Lagoon. They spend much of their time lounging on the rocks, but they also have a beautiful castle within the lagoon, described as being delicate as a goldfish's skeleton. 
Just as the fairies have sparrowmen, mermaids have mermen but they are less seen than their female counterparts. They are as handsome as the mermaids are beautiful and they share the sea maidens' vanity.
Physical Description and Biology
Never mermaids are extremely beautiful with brightly-colored eyes, scales, and hair. They are scaly all over - even their faces are covered with fine scales. Also, their hands are webbed. Some have spiny dorsal fins on their backs or tiny flippers for fingers. Mermaids range wildly in colouring-from green and gold, blue-green to amber-orange. Green is a common colour among mermaids like Oola, Pah and Soop. Mermen can have pointy ears like fairies and they can have strangely covered skin like blue. Mermaids often wear scarfs which flow around their bodies. Mermaids can also resemble women of different nationalities from the Mainland.
Never mermaids breathe underwater with gills, which they must rest above water occasionally or else they will get sore. They often do this by lounging above the lagoon's surface, but they also have a special air-filled room in their castle, known as the "wind room" for when going to the surface is not an option. Mermaids are also fast and agile swimmers and possess incredible and enchanting grace. They can also move slightly on land but only slowly like a seal.
Mermaids are incredibly snobby and will dive into the water when fairies come by. Never mermaids are not curious about other creatures. One of the few non-mermaids they will stay up for is Peter Pan, but that is only because he is the Peter Pan and therefore has snob appeal. Also, he occasionally brings them loot he steals or finds.
Mermaids are extremely vain and will sun themselves on the rocks, brush their hair and gaze into mirrors much more than a human would. They adorn themselves with glittering jewels, beautiful whalebone combs and lovely accessories, just to increase their already great beauty. Even mermen possess this great vanity.
Relationships with other Species
Not much is known about the relationship between mermaids and mortals but from the knowledge given, it probably isn't a good relationship. Mermaids probably look down on humans and can be very vicious and jealous. This is shown when Wendy came to the lagoon. The mermaids tried to drown her but were stopped by Peter Pan, the one human they like. Mermaids also play a game called Sirens sink Ships, further insinuating the bad relationship mermaids and mortals share. Mermaids would never fall in love with a human and they laugh and scoff at the story of The Little Mermaid.
Mermaids look down on fairies and will dive into the water when fairies come by. Even if a fairy helps a mermaid or gives her something she wants desperately, the mermaid will continue to look down on the fairies. Some mermaids see fairies as objects or pets and Oola and Numi once tried to keep fairies as pets. Mermaids know little about fairies and often expect Never fairies to have wands.
Though mermaids speak English quite well, they also have their own language (called Mermish) which has thirty-eight vowels and no consonants. Some never mermaids have names that can only be pronounced in Mermish.
Mermaid rank is determined by the size of their nautilus shells. The Queen has the biggest one, and other mermaids are not allowed to have one bigger.
Mermaids are musical beings and they can channel magic through their haunting melodies. It is presumed that they can mesmerize and lure men like the sirens of greek mythology. It is not safe to visit Mermaid Lagoon at night, because mermaids sing their most magical songs then. This mystical serenade makes pirates see dead sea captains, birds fly upside down, and Never fairies turn into bats.
Some mermaids have power over water, as Soop demonstrated by sending a flood to Pixie Hollow. Mother Dove also implied that Soop could send a tidal wave or sharks(hinting at a connection with aquatic fauna). Fairies never harvest water from the Mermaids' Lagoon due to mermaid magic which makes the liquid their unsuitable for fairies to consume.