Source: The Bastards of Erebus, pg(s). 76-77
A haniver gremlin is a small marine fey creature that superficially resembles a ray or skate and has an odd obsession with stealing or rearranging small items. Hanivers are less a danger than an irritation, due to their skill as pickpockets, desire for shiny objects, and curiosity to know what is inside every pocket, satchel, hat, or crevice. The gremlins have no concept of value, only desiring what others desire, and often collect items of no real value, such as pieces of glass, feathers, or bits of colored paper. The often discard the things they take, unless someone (such as the owner) expresses an even momentary desire for it. The gremlins often "trade" the items in a creature's possession for things like broken seashells and clumps of dirt. When they attempt to steal an item from a creature, it causes that creature's items to become misplaced or rearranged in unusual places.
Hanivers resemble bizarre humanoids that stand about a foot tall and weigh less than five pounds, with yellowish skin, tiny black eyes, a mouth full of needle-like teeth, and leathery skin, fins, and wings. Their wings and fins make them skilled fliers and swimmers, but otherwise they flop like a fish out of water when on land.
Habitat and ecology
Hanivers dwell in the ocean and rarely stray far from the coastline, rarely spending more than an hour out of the water, and spend most of their time skimming waves and teasing marine creatures. They rarely create lairs, but sometimes creates small hoards of their treasures in small nooks or hidey-holes. Occasionally they travel in small mobs that can frustrate ships at sea, fisherman, and other marine life. Luckily, their curiosity about closed boxes makes them easy to trap.
According to legend, hanivers fear their dead and will avoid anyone with a dead haniver in their purse or nailed over the door. Since the gremlin's flesh rots quickly, preparing such a talisman requires some leatherworking skill or other knowledge. The "candied gremlins" available in many coastal communities are in fact dried fish or rays in the shape of a haniver covered in salt and sugar.