|I know this is from The Gravedancers but my wife and friends and I all just call that movie Rape Ghost.|
This is so wrong. It is wrong three times.
First, it is true that the world is much bigger than you, and much bigger than what you think of as civilization. But it's much, much bigger than that still, because so much of the 'discovered' world is still unexplored, accounted for by mapmakers and bookkeepers but not by eyes and mouths. It is simply taken on faith because lives are short, and even eternal lives are busy. I'm throwing out a word here: ocean. Have another one: intestine. One more word: scale. Also: spacetime.
Second, there are places (and some of them quite large) where there should be something and yet there is not. There is nothing there. You may even have been through these places unscathed, because the emptiness reacts to your presupposition. It quickly makes itself look like something. But not always, never completely. What it does make is wrong. Waving grass that is really flexing, part of a single organ. Shifting dunes of gold dust. Trees with no rings, which never grew, covered in reptilian scales. You may pass by without ever noticing. You may fall victim to the perils of a hastily assembled universe. You may be there still the the nothingness exhales, empties once again, and you're not there. There's no there to be. Maybe that's where they come from.
Third, you see, are the not-people who don't live in these aren't-places. SOMEONE must live here, you reason about such places. SOMEONE would have noticed this was happening. SOMEONE would have seen. It stands to reason. There must be SOMEONE around here. SOMEONE will come for me. And so they do, greasing into being, cruel little sculptures of things. Their eyes and teeth shine like Christmas lights in the darkness, out of which they resolve themselves, their skin taking on a pale yellow, a light pink, a pastel green, a sick and off-palette tone. Their skin. It's the texture you see on the skin that forms on good chicken soup. Their eyes and rictus jaws are bright and shiny even fully formed, but they appear almost painted on. They are sculpted of one piece.
The nothingness makes these aren't-people. They're the menything. I call them Nothlings.
Nothlings are not malicious but they are incredibly aggressive, mostly out of curiosity. Once they understand you or the world around you they will watch patiently until something new and interesting happens, then see if they can kill it. They like to strangle, and have a long, steel-sharp nail-appendage on their littlest finger. They are not in proportion. They have no willy atall, but they're gross and creepy in a "guy you'd never sit next to at supper" kind of way so it's easy to think of them as male.
They don't so much have blood, or brains, or anything you'd expect, certainly not until you consciously expect it to be there. Then you'll find yourself surprised to learn they are filled with little fingers, little ears, little elbow skin wrinkles, little copies of their own faces flowing over each other like dumplings. Liquid flesh pouring from wounds and piling up in ribboned sheets on the floor.
My players spared one of these creatures when they attacked, and named him Jeffrey. They are currently in a campaign that is patient corpses, cute, widdwe mousies, and never-ending bars, bars all the way down.
It's also this.