So i came up with a Invasion of the body snatchers esk encounter where the PCs come across a town were nearly every NPC has been replaced by a changling and nearly everything has been replaced by a Mimic. The NPCs will act oddly to the players, sweeping the dirt road for example or eating plates (Things that could almost pass for socially acceptable). If the players choose to stay the night they will find themselves completely surrounded by Mimics and have to fight their way out, and any items they have bought will attack them (as they are also mimics).
Am i sadist for thinking this up?