Nightmare holds a lot of resentment towards his brother for all his teasing's about not being chosen as heir, but he acts like it doesn't bother him and plays like the dumb little brother. He may be young, but he has great ambitions, especially towards his brother, he keeps quiet around his mother, because he has greater plans in mind for his brother than what his mother would do to him if she found out, and he wants him to keep his title just a little longer.