Doctor Strange only just hit theaters internationally a couple days ago, and it's still a week away from being released in the United States. Nevertheless, at a time when studios ponder sequels long before the public sees the first movie, it's not surprising that ideas for _Doctor Strange 2 _are already being thrown around. In fact, director Scott Derrickson already knows who he would want to use as a villain in a sequel if one was green-lit: Nightmare.
When IGN asked Derrickson which elements from the Sorcerer Supreme's mythos he would want to include in Doctor Strange 2, he named Nightmare as a good candidate to be the next main antagonist. In his words:
I really like the character of Nightmare and the concept that the Nightmare Realm is a dimension. [...] That's early -- that's like the first Strange tale. I think that's in the introductory episode of Doctor Strange, and I always loved that. We decided not to do that because that's a bit of a complex idea to try to introduce everything we do introduce and introduce the idea of nightmares themselves as being a dimension. I hope somewhere down the line we do get to explore that because I think that's super cool concept
Introduced in 1963's Strange Tales #110 (the same issue where Doctor Strange debuted), Nightmare originally served the entity Shuma-Gorath, but he later escaped and became ruler of the Nightmare Realm, a.k.a. the Dream Dimension. As his name makes clear, Nightmare targets his victims though their dreams, to the point that he is dependent on their fear in order to remain powerful. In fact, if all of humanity were to suddenly stop dreaming, he would cease to exist.
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. Upon learning the ways of mysticism from The Ancient One, Stephen Strange will use these new skills to travel to other worlds. 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.
There's no word yet on a Doctor Strange 2, but considering the positive reception for Doctor Strange so far, not to mention Marvel Studios having ordered sequels for all their MCU movies besides The Incredible Hulk (and even he returned for the Avengers movies and Thor: Ragnarok), it's likelier than not that Stephen Strange will receive another solo adventure. As for the first movie, U.S. fans can see it on November 4.