I'm working on a New setting for an upcoming campaign. It's based off the semi-fact that a lot of different creatures benefit from the consumption of humanoids, but each individually needs many more humanoids to keep it alive. So what if they realized this and and decided to work together to farm humanoids. Illiathids get the brains, Vampires get the blood, Ghouls get the leftover corpses, and some other undead work in whatever else they need. I'm thinking of adding demons to get the souls, and explaining that the undead & aberration founders made a deal with a demon lord or archdevil, the souls of the farmed humanoids for a place in the Abyss in which to build a city. I'm sort of stuck now though, any ideas would be great.