!!!UNDER CONSTRUCTION!!!
A very mysterious, rarely-seen cryptid, referred to as "deep-sea merfolk" or "rainbow men". Very little is known about them, other than they exterminated sea elves and might be destroying submersibles. They have, to current widespread knowledge, never attempted non-hostile interactions with sapient species, cryptid or normal.
They usually stay away from human activity and almost never venture onto land. This has resulted in extremely scarce evidence of their existence throughout human history, and likely confusion with other mermaid-class cryptids. The advent of Remote-Operated Vehicles has revealed possible sightings within the lower abyssal zone and hadal zone. No merfolk settlement or nest has been discovered yet.
Biology
Deep-sea merfolk biology is currently completely unknown to the world at large. The SPW Foundation's cryptoecology department and the Wings Of Relief Sanctuary have partial, basic data obtained from one specimen, registered as the familiar of marine biologist Dr. Kūjō. Deep-sea merfolk are psionic cryptids, and have been categorized into the mermaid class, due to their humanoid upper body and aquatic-tailed lower body.
Thanks to their unique biology, adaptability, versatility, and complex social behaviors, deep-sea merfolk are secretive super-apex predators of Earth's oceans. They go wherever they wish, hunt whatever they want, and not even the most hostile environments or aggressive creatures will deter them. Alone or in groups, merfolk always find out some way to thrive, through body adaptations that improve their suitability for their surroundings, as well as manipulation and control of their environment. They are also clever enough to steal and alter man-made technology to serve their own purposes.
While best-suited to abyssal depths and below, they can survive in zones where even microbial life struggles. Deep-sea merfolk are one of the oldest extant lifeforms, and have existed, mostly unchanged, for over a hundred million years. They are undamaged by radiation, and never progress past their physical prime. Their bodies have intricate duplications and specializations that allow them to live virtually anywhere on Earth. Atavistic traits hidden away in their genes often re-emerge during an emergency metamorphosis, further increasing an individual's chances of survival.
Anatomy
Adaptability
Endurance and Illnesses
Abilities
Merfolk psionic and magic abilities
Ecology
Evolution
Civilization
History of the Merfolk
Legends and Myths
Culture and Lorekeeping
Belief and Ways of Life
The Old Ways
The New Way
Language
Telepathic Variants
Sigils and Glyphs
Body Language and Displays
Arts
Construction and Landscaping
Performances
Clothing and Weaving
Magical Mastery
Weaponcrafting and Armorcrafting
Cuisine
Society and Structures
The Great Clans
The Great Queens and their clans
Colonies
Tribal Pods
Schools and Ferals
Family schools and feral merfolk