A class assignment where we had to over the course of a few weeks develop a creature. I developed a sort of sky whale looking thingy. It floats about by metabolzing hydrogen from its food into airsacks on its back, its propulsion comes from moving its fins and tail. They communicate through a mixture of noise and bioluminescence. They are omnivorous and will adjust their bouyancy to bite off large chunks off mountainsides where they smell anything organic. They can digest rocks, but prefer the taste and nutrition of organic matter. Prior to coming by for a meal, a skywhale will regurgitate a portion of its previous meal over its new meal as well as certain powerful enzymes. As the regurgitated matter is very acidic, and it takes a while for the sky whale to orient itself for its meal anyway, the end result is that a lot of the matter is broken down and much of the rocks are softened, making the meal easier to consume.
For a sense of scale, there's a 18wheeler fuel truck being regurgitated somewhere in the black rain.