Boneless

The boneless are great flopping sheets of skin that fly in search of prey. They move through the air as a manta
ray swims through the ocean. Their hides match the complexion of human skin. A pair of human-looking eyes
is mounted front and center on its top surface. Anyone foolish enough to closely examine a boneless will discover vestigial remnants of its original human form scattered randomly about its hide - an ear, a few teeth, some hair, a nipple. Along its underside they'll find hundreds of enlarged pores about a fifth of an inch in diameter. In living specimens each pore will be sealed with a layer of yellow mucus.
Boneless are strictly carnivorous. They'll prey on any large animal - moose, deer, bear, cougar, monster - but prefer human meat if they can get it. They attack by wrapping themselves around a victim and slowly smothering him to death. It's a horrible way to go: the boneless begins to digest its prey before it's even dead. As soon as the boneless is wrapped around its victim, its pores begin to secrete concentrated digestive acid. This melts the victim's flesh, allowing the boneless to absorb the resulting fluid back through the pores.
Although the acid retains its potency after the boneless dies, most people don't bother to harvest it. Because it's a dangerous product to obtain, they avoid becoming dependent on its use.
Boneless are instinctive, not intelligent. When hungry, they search for prey. They are usually solitary hunters. When full, they find a sheltered spot - in a tree, tunnel, or cave - and sleep for weeks at a time, rolled up or curled into a ball. On rare occasions a few might be sighted together, for no clear reason - they don't breed and seem incapable of communication. In fact, they sometimes attack one another. A fight between two boneless is a remarkable sight, as each tries to envelop the other in a death squeeze. Often both die, tangled in a partly-digested mass.
Survivors of boneless attacks may have recurring nightmares in which they're being smothered or burned 
by acid. They might develop phobias against blankets or bathing.