Classic Costumes

Some characters have classic outfits that resemble the classic X-Men characters:

Wolverine: Costume VII
Betsy: Costume VII
Forge: Costume VI
Gambit: Costume V
Juggernaut: Costume VII
Magneto: Costume VII
Nightcrawler: Costume VII
Sabretooth: Costume III
Rogue: Costume VI 

Eighth Costume

Win forty matches in survival mode as any character.

Seventh Costume

Select team mode and choose to fight with eight characters. Defeat all of the your opponent's team by using two or less of your own fighters to unlock the seventh costume for the character(s) you used. Wolverine gets his original yellow/blue/black costume. Phoenix gets a red/gold costume similar to Dark Phoenix. Juggernaut, Gambit, and Psylocke get a costume similar to their comic book original. Beast gets a blue costume with a yellow X on his chest, and he also has a helmet. When you chose the seventh costume for Cyclops, Wolverine, Betsy, Juggernaut, Sentinel A (Sentinel), Gambit, Storm, Sabretooth, Rogue and Magneto, they will most commonly appear in their costumes if they were in a "Vs." series game (Marvel vs. Capcom: Clash Of The Superheroes, X-Men vs. Street Fighter, X-Men Children Of The Atom, Marvel Super Heroes vs. Street Fighter).

Fifth Costume

Successfully complete the game in arcade mode under the hard difficulty setting with all characters.

Sixth Costume

Defeat all ten fighters in time attack mode in under fifteen minutes to unlock the sixth costume for the fighter you selected.

Fourth Costume

Win twenty matches in survival mode with all characters.

Third Costume

Successfully complete the game in story mode to unlock that character's third costume.

Fight As Pyro

Successfully complete the game in arcade mode as Dark Phoenix under the easy, medium, and expert difficulty settings to unlock Pyro as a selectable character.