I've been trying to come up with a name for the creatures that exist in the depths of the ruins of Esterfay. I would like to share some information here without spoiling anything in the campaign.
When I started making the ruined halls I wanted there to be something very alien, something very old, that were the original architects of the halls. The place would have been basically a giant strip of fly paper for them to catch civilizations in to feed their inhuman hunger.
The weird stuff that exists within the halls is a product of their madness leaking to the surface. Some of the weird things were created by mad wizards falling prey to these dark creature's malign influence. Others were created by the creatures themselves, to lure in the greedy, vain and prideful.
The other reason I made the Dwellers in the Dark? I love Mind Flayers and Beholders, but they are totally owned by Wizards of the Coast. I wanted something that I could call mine. Something I could do anything with and mold into the antagonists I wanted in my game.
Description: The Dwellers in the Dark are a few feet taller than a man, but irregular and slender. Above their shoulders resembles a snakes, long and serpentine, with no disenable difference between neck and head. Eyeless, with a pair of wicked mandibles framing a sucker-faced jaw of many rows of circular teeth. They have four arms and two legs, their shoulders and joints pointy yet thin. Their skin is scaly and slick, often colored pale white, indigo or other bizarre, unnaturally bright or pale colors (Weird Lizard Colors). They dress in robes most often, but the more martial members of the race wear strange proto-organic armor that makes them blend in with the darkness as they move.
Combat and Powers: I don't want to get too much into this, for fear of giving too much away. The Dwellers are very strong physically, but often prefer to use their potent magical abilities on their victims. One such power they have developed is a powerful defense mechanism. They can force their skin to flicker brightly, emitting a blinding hypnotic flicker of light that causes sighted creatures to make a will save or become paralyzed by their own nervous system going into shock.
Some sample magical abilities, in no particular order: Charm Person, Command, Paralysis, Sleep, Detect Magic, Invisibility, Spider Climb, ESP, Magic Missile, Lightning Bolt, Magic Shield, Teleport
Of course, individual powers will vary.
Servants of Flesh and Spell: The Dwellers in the Dark make things. Spell and flesh woven together to create servants to enact their will upon the sighted world above. They make their madness manifest in an assortment of ways, and no two things are exactly the same. That said, they have some "common" creations that they use to serve them.
- The Sightless Hounds - Pale slime skinned hounds the size of a horse, that can run down prey for the Dwellers. A single pack typically serves a single Dweller. They are deadly, with a poisonous bite and vicious claws. Many appear mutated in strange ways - faces on their hides that scream in pain and beg for death; tentacles covering their hide, grasping and pinning those they fight; or strange appendages and spikes.
- The Crawling Madness - Deadly worms that first appear as tiny parasites too small to see. The Dwellers have released these parasites into much of the drinking water, and they can also be transmitted via bodily fluids. An infected individual first appears to have their eyes "Swimming with madness" as the worms multiply quickly in the body. They grow stronger, gaining bonuses to their strength and stamina, as well as growing smarter, gaining bonuses to intelligence. Their bodies begin to mutate as the worms reweave their flesh from within. Soon, they become so insane with bloodlust that they attack on sight anything that is not under the control of the Dwellers. A rare few will be chosen by the Dwellers to undergo the Apotheosis, and be transformed into Dwellers themselves.