Of all the comic book movies currently being lined up for phases two and three of Marvel's cinematic universe, Doctor Strange might be considered the most anomalous. So far, the screen mythology has largely been leaning towards science-based explanations for the extraordinary happenings, with even Thor and Loki's powers described as having as much to do with science as they do magic.
Doctor Stephen Strange, however, deals mainly in mysticism and magic, acting as Sorcerer Supreme and protector of Earth from equally mystical forces. As such, it will be interesting to see how Marvel movie mastermind Kevin Feige orchestrates the blending of Doctor Strange's tone with that of, for example, Iron Man or Captain America, and whether Strange's enemies will end up clashing with characters from the current live franchises.
With the release of Doctor Strange still so far off, details are currently scarce. However, the Latino-Review has published a report stating that the Doctor Strange movie will have three different villains from the comic books: Baron Karl Mordo, powerful sorcerer and fellow disciple of the Ancient One; Dormammu, an ancient being from another dimension and one of Strange's fiercest enemies; finally, a giant version of the Mindless Ones, a race of beings with incredible strength but no will of their own, who act as agents of pure destruction for whoever controls them.
El Mayimbe claims that he has read Thomas Donnelly and Joshua Oppenheimer's script for the movie, and says that it is "fantastic" - though he doesn't give any actual details on the villains beyond naming them and saying that Dormammu will be the primary antagonist and Karl Mordo the secondary. Since that script was written a while ago, however, and phase three of Marvel's cinematic universe is still a couple of years away, the current story should by no means be considered locked, and may be impacted by other events that unfold within the shared universe between now and the beginning of production.
Having said that, these are by no means unlikely choices for the villain roles of Doctor Strange. Both Dormammu and Karl Mordo are arch-enemies of the superhero, so speculating that they might make an appearance is about on par with suggesting that the Green Goblin will be in a Spider-Man movie. The Mindless Ones are also a fairly obvious choice to carry out minion duties, so it wouldn't be surprising to see them show up to do Dormammu and Mordo's legwork.
For now, take this rumor as just that: a fun talking point to pass the time between now and the eventual, far-off release of Doctor Strange.
Thor: The Dark World arrives on November 8th, 2013, Captain America: The Winter Soldier on April 4th, 2014, Guardians of the Galaxy on August 1st, 2014, The Avengers 2 on May 1st, 2015, and Ant-Man on November 6th, 2015. Doctor Strange is expected to be the second movie in Marvel's phase three, but a release date has not been settled upon yet.
Source: Latino Review