Nautatius

The airship's crew rejoices -- a skyberg has been sighted, which means a chance at solid ground, fresh food, and perhaps some clean water. Too late do they realize their error as their vessel is ripped apart by enormous tentacular appendages, and they are dragged screaming one by one into the cavernous maw below.

Lurking Giant. The Nautatius lies in wait, disguised as a skyberg -- one of the world's many inexplicable floating islands. Rather than providing a safe place to land for weary crews, however, it instead ambushes airmen, devouring them and their craft.

Uneasy Rider. A Nautatius only needs to feed once every month or so, though it truly gorges itself on such occasions. A satiated Nautatius will tolerate creatures on top of it until it grows hungry again, allowing savvy airmen to use the lumbering beast as a temporary, if treacherous, conveyance.

Gastric Maw. A Nautatius's mouth doubles as its stomach - prey is slowly digested and chewed at the same time, with the putrid fumes being siphoned off to fill the enormous floatsac that buoys the creature. Nutrients swirl within its saliva, nourishing the symbiotic algae and platlife adorning its hide and allowing it to camoflage itself as a normal floating island.

Rare and Valuable. Deceptive and dangerous though they may be, a slain Nautatius can provide many lucrative resources to the enterprising monster hunter. Nautatius ivory is acid-resistant and immune to corrosion, while its nutrient-rich saliva (and several mysterious fluids claiming to be such) is hawked as a health-fortifying supplement. The creatures' inestimable age means they often sport species of plant and insect on their backs long extinct elsewhere in the world. Some sky pirates even patch the slow leaks in dead Nautatius floatsacs and strap sails or engines to the poor beast's crown, turning the corpse into a grisly and reslient strike craft.

Image source: Capcom, Monster Hunter 2