An update for Marvel Vs Capcom 3 is now available for the Xbox 360 and PS3. The main purpose of the update is to add Event Mode, which is a series of special challenges. Event Mode won't be live until March 25.
The update also addressed some balancing issues, specifically for Marvel's Sentinel. Sentinel is thought to be the most powerful character in the game with powerful attacks, lots of health and relatively easy controls. The patch decreases Sentinel's health from 1,300,000 to 905,000. OMG! Nerf!