The two join James McAvoy, Michael Fassbender, Alice Eve, Nicholas Hoult and Caleb Landry Jones in the Matthew Vaughn-directed film, hitting theaters on June 3, 2011. Variety lists Aaron Johnson as part of the cast as well, but he has yet to be confirmed.
X-Men: First Class, following the classic Marvel mythology, charts the epic beginning of the X-Men saga. Before Charles Xavier and Erik Lensherr took the names Professor X and Magneto, they were two young men discovering their powers for the first time. Before they were archenemies, they were closest of friends, working together, with other Mutants (some familiar, some new), to stop the greatest threat the world has ever known. In the process, a rift between them opened, which began the eternal war between Magneto’s Brotherhood and Professor X’s X-Men.
Mystique was played by Rebecca Romijn in the first three "X-Men" films. Watch a clip of her from X-Men: The Last Stand below: