|All you need to do is defeat the opponents team within 15 seconds , I suggest you do this with a partner or with a second controller. |
Go into the Game Settings and set the timer to 30 seconds and the Damage level to 4. Before picking the characters, set your handicap to the highest level and your opponents to the lowest level. Pick Magneto (and any other unneeded characters) against 3 Rolls use Magneto's + against the team for a fast victory. If the timer hits 15 seconds then try again, however that shouldn't be the case.
IGN Walkthrough Video