The Monstrosity is a fictional demon in the prime reality of the Marvel universe of Marvel Comics. Which was created in 1993 by Chris Cooper, first appearing in issue #13 of the 1st volume of Darkhold: Pages from the Book of Sins.
The Monstrosity is a demon released by the Darkhold, which the press called "Monstrosity". Which possessed superhuman strength, durability, and speed. Able to easily life a tall muscular man with both hands above its head and throw him. It's claws could easily tear human flesh and bone, and rip through a car's roof. The demon siphoned the lifeforce of humans via its mouth, killing them. Usually it left a shriveled corpse.
For every lifeforce that it consumed it gave the one who used the Darkhold page the lifeforce to heal another being. Victoria Montesi for a short period was able to heal her hospitalized lover because she used one of the pages of the Darkhold, not realizing that it released a demon which was killing and stealing their lifeforce for her use. Many were killed before she discovered the truth and rejected the Darkhold.