One who waits

A nameless creature described as the one who waits lingered in an unknown planar location thought to be somewhere in the Nine Hells.

Description
The creature was a gargantuan slug- or worm-like monstrosity, grotesquely fat and sickly green. It had at least three stubby arms, and was topped by a disgusting face, with pointed ears, red eyes, flaring nostrils, and a massive drooling mouth with many fangs.

Personality
The one who waits seemed to be rather incurious and lazy. It spoke very crudely.

Relationships
The creature was attended by a swarm of flying creatures: gargoyles and kenkus. It seemed to serve or worship the god Bane, Lord of Tyranny.

Realm
Its realm in the Hells was an enormous cavern, where fire seeped from caves and ponds of pale green liquid lay on the ground, and where vapors rose.

History
It appeared that the creature had simply lain atop its massive throne for thousands of years, waiting and wishing for power.

Then, at last, in the Year of the Prince, 1357 DR, one side of the subverted Great Door appeared in its realm. It thanked Bane for the gift of power—it cared not to think about why or how—and the awful creature and slithered toward the Door, intent on wreaking havoc on the Material Plane. Its swarm of kenkus and gargoyles flew on ahead. These caused havoc in Waterdeep and around the site of the Great Door.

When the worm-like creature at last emerged through the Great Door, the wizards Kyriani Agrivar and Parwyyd Hanifar used telekinesis to first open the door wide and let it through, then slammed it shut on its trunk, slaying the monstrosity. Parwyyd then destroyed his Great Door with a disintegrate spell, and the threat it posed was ended.