We are already excited for Phase 3. However, there is the much anticipated Ant-Man movie that will wrap up Phase 2 on a high note. Now that Phase 3 is taking its beginning shape with Captain America: Civil War, there will be a whole new world to explore, the Cosmic world, in Doctor Strange.
It is already confirmed that Benedict Cumberbatch will play the lead role: Stephen Strange. But we do not know any other actors involved in this project. There were rumors that the Ancient One, a Tibetan mystic who is Stephen Strange's mentor, will be played by actors like Morgan Freeman. Now, according to the Hollywood Reporter, Tilda Swinton is in negociations to play the Ancient One in Doctor Strange. In the comics, the Ancient One is an old man: the casting of Tilda Swinton is very surprising considering that he is, first of all, an old man.
On Scott Derrickson's twitter, we see a photo, posted recently, that can indicate the possibility to see Death in the movie.  Death is female and is well known to be the love interest of a mystery and powerful purple man: Thanos. Death can be a key element in Phase 3: she can be the reason why Thanos is now searching for the Infinity Stones. I am not sure that Tilda Swinton could be the Ancient One, but can she be Death? What are your theories? Will Tinda Swinton appear in Doctor Strange. It will be official when Tilda Swinton or Marvel Studios will confirm the casting.