Osyluth

The osyluth - also called a bone devil - is a gaunt-looking devil that appears in Dungeons & Dragons, most notably in the Forgotten Realms campaign setting. These horrific monsters serve as the lawkeepers of the Nine Hells, enforcing the rules of the Lords of the Nine and torturing those who dare to disobey. Osyluths delight in the suffering of others, either mortal or devil.

Physiology
Osyluths are humanoid devils that stand on average at 9 feet tall. They have gaunt, wiry bodies with pale skin stretched taut over their skeletal frames, their digits each ending in razor-sharp claws. The osyluth also possesses a long, bony tail similar to that of a scorpion, ending in a scythe-like bladed tip.

Abilities

 * Fear Aura - Osyluths compel any creature that approaches them into a state of panicked terror.
 * Wall of Ice - An osyluth can conjure icy barriers at will to keep its enemies divided.
 * Poison - Exuded from the stinger on the creature's tail.
 * Flight - Some osyluths have wings, though they can still fly without them.
 * Summon Devil - Osyluths can summon lesser devils to aid them in battle.
 * Invisibility - An osyluth can make itself undetectable to the naked eye.
 * Immortality - As a type of devil, osyluths cannot be killed by mortal weapons or spells. They can only be banished from the mortal plane back to the Hells from whence they came.