Concept: a D&D campaign where every party member has been co-opted or replaced by some sort of hostile intelligence; e.g., the fighter has been possessed by a ghost, the wizard is being mind-controlled by her sapient magic ring, the rogue is actually a shapeshifting blob-monster who devoured the original and stole her form and memories, and so forth. Each of them is totally unaware of the others, and believes itself to be the only monster in a group of unwitting human adventurers.
- The warlock has been infested by a demonic fungus; her ridiculous hat conceals the giant mushroom growing from the top of her head.
- The barbarian is a lizardman who fell victim to a botched reincarnation spell and regenerated as a human.
- The druid was actually killed weeks before the party met, and is being expertly impersonated by three dire raccoons in a trenchcoat.
- No one knows that the bard’s deal is; she seems perfectly normal to every physical and supernatural test, but pings to detect aberration.