Marvel Vs. Capcom

Beat 'em While They're Down
After defeating your opponents, press and hold START. You will be able to move freely and hit your opponent, you can even do a Super on them.
 
Change Battle Order
At the Vs. screen press all 3 P or K buttons, again to swap back.
 
Choose Your Helper
To obtain the helper of you choice, hold START and then the designated buttons (below) to choose your second character. 

Normal Helpers

Unknown Soldier  LP           Can be used 4 times

Lou              MP           Can be used 8 times

Arthur           LP+MP        Can be used 8 times

Saki             HP           Can be used 7 times

Ton Pooh         LP+HP        Can be used 9 times

Devilot          MP+HP        Can be used 5 times

Anita            LP+MP+HP     Can be used 5 times

Pure and Fur     LK           Can be used 5 times

Michelle Heart   LP+LK        Can be used 6 times

Thor             LK+MP        Can be used 8 times

Cyclops          LP+LK+MP     Can be used 7 times

Magneto          LK+HP        Can be used 7 times

Storm            LP+LK+HP     Can be used 6 times

Jubilee          LK+MP+HP     Can be used 8 times

Rogue            LP+MP+HP+LK  Can be used 6 times

Psylocke         MK           Can be used 5 times

Juggernaut       LP+MK        Can be used 3 times

Iceman           MP+MK        Can be used 4 times

Colossus         LP+MP+MK     Can be used 5 times

U.S. Agent       MK+HP        Can be used 5 times



Secret Helpers

Shadow           LP+MK+HP     Can be used 3 times

Sentinel         MP+MK+HP     Can be used 4 times
Steal Helper
After beating the 2nd opponent but before the pose points counter appears hold all three K buttons. You'll have your opponent's helper at the start of the next battle.
 
Change Ryu’s Gi Red (and get Kens moves)
Choose Ryu as one of your characters. In game get level one power and perform half circle from forward to back followed by MP.
 
Change Ryu’s Gi Grey (and get Gouki's moves)
Choose Ryu as one of your characters. In game get level one power and perform half circle from forward to back followed by HP.
 
Note: To change back to normal Ryu in the above 2 codes, push LP instead of MP or HP. You can inter-change also.
 
Play as Lilith style Morrigan
On character selection highlight Zangief and then follow these directions to make her appear below War Machine. Lx2, Dx2, Rx2, Ux2, Dx4, Lx2, Ux4, R, L, Dx4, Rx2, Ux4, Lx2, Dx4, R, D.
 
Play as Gold War Machine
On character selection highlight Zangief and then follow these directions to make him appear above Zangief. Lx2, Dx2, Rx2, Dx2, Lx2, Ux4, Rx2, Lx2, Dx4, Rx2, Ux2, Lx2, Dx2, Rx2, Ux5.
 
Play as Orange Hulk
On character selection highlight Chun Li and then follow these directions to make him appear above Chun Li. Rx2, Dx2, Lx2, Rx2, Dx2, Lx2, Ux4, Dx2, Rx2, Ux2, Dx4, Ux4, L, U.
 
Play as Red Venom
On character selection highlight Chun Li and then follow these directions to make him appear above Chun Li. R, Dx4, L, Ux4, Rx2, Dx2, Lx2, Dx2, Rx2, Ux4, Lx2, U.
 
Play as Roll
On character selection highlight Zangief and then follow these directions to make her appear above Megaman. Lx2, Dx2, Rx2, Dx2, Lx2, U, R, Ux2, Rx2.
 
Play as Shadow Lady
On character selection highlight Morrigan and then follow these directions to make her appear below Gambit. U, Rx2, Dx4, Lx2, Ux4, Rx2, Lx2, Dx2, Rx2, Dx2, Lx2, Ux2, Rx2, Ux2, Lx2, Dx6.
 
Fight Hyper Venom
Get first Attack in all stages and finish off your opponents with at least 4 two on one duo team attack without losing a character.
 
Fight Shadow Lady
Same as Hyper Venom above but you need to completely use all your helper stocks for at least 4 rounds.
 
Fight Gold War Machine
Get first Attack in all stages and finish off your opponents at least 4 times in double attack mode without losing a character.
 
Fight Orange Hulk
Get first Attack in all stages and finish off your opponents at least 4 times with any type of super move without losing a character.
 
Fight Lilith
Same as Orange Hulk above but use your helper 4 times a match.
 
Fight Roll
Get first Attack in all stages and finish off your opponents with at least 3 two on ones and use all helper stocks for at least 4 rounds without losing a character.
 
Freeze Your Opponent
To freeze your opponent, use Venom and Spiderman. Build up your meter to level 3, do an infinite combo attack, then use fierce throw with Venom to catch your opponent in web. Right when you do that throw Spiderman's web ball (fireball). If you're fast enough, you should have double webbed the guy and he can't move until you hit him. Now you have all the time in the world to build up your meter and do whatever you want.
 
Invincibility
Choose any two characters. Let your first charater die on the first match. When the second character come in, make sure he is hurt until he can only have a pixel of energy. After that, finish your special partner and throw a super. Finish the match. From the next match until the end of the game, you are immune to any kinds of hits.
 
Megaman's 1000 Point Cheat
After beating the other team with Megaman, press START and do Megaman's super (Hyper Megaman). The background will change and the number 1,000 will be shown on Megaman's chest.
 
Megaman's 50,000 Point Cheat
After beating the other team with Megaman, press START and do a Beat Plane when the point total starts. If done correctly it won't fade away and you will see the 50,000 point announcement come up.