Marvel vs Capcom 2/Miscellaneous
Switching Characters at the Vs. Screen
Additionally, the order in which the player picks his team can be altered during the "Vs." screen. By holding down the assist 1 button, the player can swap the first and second characters shown during the loading screen. Holding down assist 2 results in swapping the first and third characters shown during the loading screen. Holding down both assist buttons swaps the second and third characters.
Note that this trick is intentionally disabled for online play.
The First Attack Glitch
By swapping your starting character during the Vs. screen you activate a glitch. Once activated it allows you to hold any of the four attack button and when the fight begins, if it's still held those attack buttons will automatically come out. Bear in mind though it is said a perfectly timed attack is more accurate than using this glitch, so don't always expect to get away with it at high level play.
Typically it is most advantageous to 'glitch' something very quick such as Magneto's 1-frame cLK, but you can also glitch a dash (2P - you can glitch either a forward or back dash), a switch-in (LP+LK or HP+HK), or a button-only special move such as Storm's Lightning Attack.