His fourth one is randomly chosen, and he may sometimes spawn with more. He has three traits that are always present: evil, mean and dastardly (from his aspiration).
If Sims are cursed again, a new Night Wraith will be generated. However, players can get around this restriction by removing the curse and then reloading the lot. He is always feeling very sad, and cannot be interacted with normally. Night Wraith is an NPC that will stalk and scare any spellcaster who has the Curse of the Night Wraith.
