"You promised me that you wouldn't let magic take you away from me. I didn't raise you to be a boy who would break a promise to his Mum. You must come back safely, because you promised"

It does sound somewhat off-putting out of context. However, she wants him to be safe, and she knows him well enough to realize that the best way to make him want to be safe is not to appeal to his own self-preservation instinct, but to his sense of duty and responsibility. This desire to keep your child safe might be selfish, but it is hardly indicative of narcissism. Most loving parents, especially mothers, would go to some length to keep their underage child out of mortal danger. If this requires some blatant guilt-tripping, so be it.