The titular ability of Nightmare is his ability to seem in dreams, possibly prior to the target had encountered him in the flesh inside of a form of sick omen or within the minds of survivors following a terrifying assault. He can shift into the astral and ethereal planes. https://gogogobookmarks.com/story19796255/the-smart-trick-of-nightmare-mu-online-season-20-that-no-one-is-discussing