Nightmare is the guardian of negativity. So naturally he gives off a really negative aura. Nightmare has a very sneaky, manipulative and sinister character, he scares people around him. Even his team members. But no one can deny the fact that he is a very good strategist and a good leader. He fights for negativity and has 4 tentacles that allows him to fight without weapons. He also has a slimy skin that somehow doesn't stick around. And that makes him more mysterious.