First, the Capcom characters.
Arthur is the short protagonist in the Ghosts and Goblins franchise. In it, the knight ventures through dark, horror-filled caverns and worlds in order to save the land from destruction, as well as the princess along the way. Unfortunately, getting hit loses his armor layer by layer, but he will fight hard even in his skivvies. His specific weapon of choice is the lance, but he also uses other items in his arsenal as they appear.
Nathan Spencer is the lead character in the Bionic Commando franchise. Also known as RAD Spencer, he is an elite operative with a special bionic grappling arm which can grab just about anything in order to get him to his target. The series remained fairly small until its rebirth in 2008 with Bionic Commando: Rearmed and its retail sequel, Bionic Commando. A sequel to Rearmed is scheduled for next year, and in MvC3, he's in his 2009 digs.
Now for Marvel's side of the bargain.
MODOK (standing for Mental Organism Designed Only for Killing) is a major, reoccurring villain in the Marvel comic world. Originally a technician for the organization AIM, he is given great intellect equal to that of a computer, and he has become so smart that he can estimate happenings almost to the point of being a psychic. His head is so large, however, that he is forced to remain in an flying chair, equipped with a large variety of weaponry.
Magneto is the main reoccurring villain in the X-Men franchise. A long-time friend of Professor Xavier, Magneto (born Max Eisenhart) is a mutant with the ability to create magnetic fields, causing him to ultimately have control of any and all metals. After a multitude of heart-wrenching events in his life, he chose to support mutants by having them fight against human oppressors rather than cooperate with them, as Professor X preferred. Since then, the two have been at odds, with Professor X's X-Men and Magneto's Brotherhood of Mutants.
Here is some footage of the Capcom characters in action.
Marvel Vs. Capcom 3: Fate of Two Worlds is expected to release in 2011 for Xbox 360 and PS3.
SOURCE: Marvel.com and Capcom Unity