Most are between 4 and 5 feet long, though some have been seen at sizes such as 7 feet long, with a fin pattern on its sides and top.
Their ability to fly relates to pouches beneath their wings, containing lighter-than-air gas, that deflate when diving.
They seek fish just below the water's surface, of crabs and rats on the docks, and aren't nearly as graceful on land.
The skyeel will find prey from above either a fish in the ocean or a rodent or small crab on the ground. It will pounce downward in a sharp dive, releasing the gas from its pockets and grabbing the crab or rodent in a kind of rolling pounce across the ground. It will curl up and eat its prey, then will wiggle off to a hole or hollow somewhere to rebuild its gas pockets (which can take an hour or two to fill back up.)
Skyeels are not afraid of humans.
Skyeels are graceful and fluid in the air, often accompanied by many tiny spren, flying around them in a swarm. Sailors often refer to them as luckspren. It is unlikely that they are truly luckspren.
According to Inkthinker's notes, skyeels are often accompanied by tiny blue spren in the shape of darting, arrowhead like fish. It is thought that the spren somehow help skyeels fly.
These spren appear like small glowing arrows in schools. Individuals drift away and vanish like small plumes of smoke rising into the air. They dance around the live chasmfiend and are a source of light.