X-Men vs. Street Fighter

Fight as Akuma:
Highlight Magneto, Juggernaut, Dhalsim, or M. Bison at the character selection screen then press Up. If done correctly, Akuma will appear.

Fight as Shadow:
Highlight Dhalsim at the character selection screen, then hold Up for about ten seconds and press LP + MP + HP.

Fight as The Hulk:
Highlight Cyclops at the character selection screen, then press Down four times. Highlight Wolverine, then press Right twelve times. If done correctly, The Hulk will appear next to Wolverine.

Fight as Alpha Chun-Li:
Highlight Chun-Li at the character selection screen, then hold Start and press any Punch or Kick button.

Random fighter:
Highlight any fighter on the left or right edge of the character selection screen, then hold the Joystick away from the center of the screen. Note: You can also fight against the same character by getting the random selection to stop on the originally highlighted fighter.

Same character match:
Place the pointer to the left or right of the character you wish to have two of. Move the pointer onto the character and hold the Joystick so that the cursor begins to scroll via the "Random Character" function. Then, select that same character by manually timing it. The pointer will reappear on that character, allowing you to select it again.
Information in this section was contributed by el may.

Alternate costumes:
Highlight a character at the character selection screen then press a Punch button for a darker costume or Kick for a lighter costume.

Change to second character:
Hold Start + LP + MP + HP after selecting your characters. Release the buttons when the match begins to use your second character.

Continue attacking:
Press Start immediately after winning the match to continue hitting the defeated character.

Hint: Rogue: Additional winning pose:
Select Rogue as one of your fighters. After using her to defeat an opponent (without a team super), hold LP + MP + HP or LK + MK + HK before she does her normal win pose.

Hint: Rogue: Kisses girls:
Select Rogue as one of your fighters and do her special punch combo where she tosses you in the air against a girl that is controlled by player two or the CPU. Rogue will do her punch throw combo and then fly up and kiss the girl on the mouth.
Information in this section was contributed by Kermit151.