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).