Consider the idea of spontaneous genesis of life, as used to be belived. What strange kinds of life might arise from modern substances? What kind of vermin would a landfill produce, or an oil spill on the ocean?
A demon who isn't some hideous creature bent on consuming souls, bu is, in fact, a likable chap who enjoys having pleasant chats with people - trying to talk them into becoming his servants.
Thieve's House or thier main front: All the floors are designed to squeak when stepped upon or to sag or bend sending a small shake along the beam, somewhat like a spiders web, to alert those inside.