(Or: an Unreliable Narrator taken Beyond the Impossible.) Say, for example, you were writing a horror story. (What I'm currently brainstorming isn't this, but the problem is the same.) A group of teenager investigate a supposedly haunted house, spooky stuff happens, but eventually it turns out that it was probably all caused by some insane murderer and the ghosts merely manifested as a representation of the protagonist's personal insecurities; the ending is ambiguous on this point. How could you write a chapter or two from the point of view of a ghost, treating them as a narrator and developed character, while still questioning their existence?