Bryan Singer posted another photo from the set of X-Men: Days of Future Past on his Twitter account, and it came with the caption, "Man on Wire." As you can see, it features one of the characters from X-Men using his mutant powers. I think it might be Michael Fassbender as Magneto.
Starring Ian McKellen, Hugh Jackman, Patrick Stewart, James McAvoy, Michael Fassbender, Jennifer Lawrence, Nicholas Hoult, Anna Paquin, Ellen Page, Shawn Ashmore, Peter Dinklage, Omar Sy, Halle Berry, Daniel Cudmore, Fan Bingbing, Evan Peters, Josh Helman and Boo Boo Stewart, the mutant ensemble hits theaters on May 23, 2014.
The film is based on the comic book storyline "Days of Future Past," which ran in Uncanny X-Men #141 and 142 back in 1981 during Chris Claremont and John Byrne's run and introduced the idea of an alternate future for Marvel's mutants that grew out of the Brotherhood of Evil Mutants killing an important senator, leading to a future where all mutants are hunted by Sentinels.