World: Alfheim, small populations in Midgard
Diet: Mostly fish and squid
Length: Varies wildly
Lifespan: 100 years
Activity Cycle: Diurnal
When most people think of mermaids, what comes to mind is more like the beautiful undine. Their bodies are a colorful amalgamation of fish and humanoid, scaled on both ends. While mermaids are natural creatures of Midgard, the undine are fae and inherently magical. When in danger, an undine can temporarily become one with the water around it, intangible and invisible for a few seconds while it escapes.
Undines are one of the most variable species possible, each one resembling a different fish seemingly at random. Adults of the species can range from a couple inches to the length of whales, and can have spines, camouflage, or any other odd feature a mundane fish may have. There is no continuity in features from parent to child, and few members of the species even know their parents. Every year, undines move from the oceans to rivers, swimming far upstream to great mating grounds. There they will create the next generation. They have a reputation for even mating with other beings, and there are rumors, but no confirmed examples, of hybrids born of these unions.
Their children are born alone as regular fish, unaware of being anything more for a few years before they begin to gain undine features and abilities. Once they are large enough, they leave the streams and leave to find a tribe in the ocean. They will settle with other Undine made for the same environments, with very different tribes around reefs, the open ocean, and more exotic locations of the sea. Some say there are even bizarre undines of the deep who never return to streams for spawning, but nobody can travel so deep and live to tell the tale.