Nightmare is pure evil, a former guardian of negative feelings and the self-proclaimed King of Negativity. Nightmare embodies everything bad: he is egocentric, manipulative, abusive, sadistic, etc. Despite this, Nightmare is not stupid. He is intelligent and patient when it comes to getting what he wants. He completely despises positive emotions and avoids feeling them because they make him feel weak and remind him of who he used to be. Nightmare wants to destroy the entire multiverse.