Upon learning the ways of mysticism from The Ancient One, Stephen Strange will use these new skills to travel to other worlds.
Along with fully introducing magic into the Marvel Cinematic Universe, Doctor Strange 2 is also delving into alternate dimensions, where the same laws of reality don’t apply.
He’ll have enough on his plate in this first movie dealing with Kaecilius, but it stands to reason that eventually, the Master of the Mystic Arts might find himself in Nightmare’s world and have to do battle with the malevolent entity.