Personality. Nightmare! Sans is, in general- sadistic. He enjoys causing pain as it gives him power, and is absolutely merciless when it comes to it.,nightmare Super Genius as he has read almost every book in his library, traveled to countess different universes, and has been around since the last guardian of positivity meaning he's most likely been around thousands of years. Error!Sans is an AU destroyer., In this AU, he is bent on destroying all AUs and things he considers 'glitches' or 'mist’