In a completely separate announcement from Sir Arthur & Nathan Spencer, Marvel vs. Capcom 3 gets Magneto & M.O.D.O.K. to join the ranks.
They join the rest of the Marvel Characters in Marvel vs. Capcom 3: Spider-Man, X-23, Dormmamu, Thor, Deadpool, Hulk, Wolverine, Iron Man, Captain America, Doctor Doom and Super-Skrull