At the character selection screen or when the game is paused, press Down, Up, Down, Up, Right, Down, Right, Left, Start.
Play as Deadpool:
Successfully complete the game.
Play as Iron Man:
Find the four homing beacons in Act 1 through 4 and collect the piece of his armor that each set unlocks. Then, save Iron Man after finding the four homing beacons in Act 5.
Play as Professor Xavier:
Successfully complete all Danger Room missions.
At the character selection screen or when the game is paused, press Left, Left, Right, Left, Right, Up, Start.
At the character selection screen or when the game is paused, press Up, Up, Up, Down, Up, Down, Start.
At an Xtraction point, while at the character selection screen, press Up, Down, Up, Down, Left, Up, Left, Right, Start.
At an Xtraction point, while at the character selection screen, press Left, Right, Left, Right, Down, Up, Start.
At an Xtraction point, while at the character selection screen, press Right, Left, Left, Right, Up, Up, Up, Start.
All Danger Room courses:
At the Danger Room course menu, press Right, Right, Left, Left, Up, Down, Up, Down, Start.
At the Review Menu, press Right, Left, Left, Right, Up, Up, Right, Start.
At the Review Menu, press Left, Right, Right, Left, Down, Down, Left, Start.
All concept art:
At the Review Menu, press Left, Right, Left, Right, Up, Up, Down, Start.
All Character Skins:
At the team management screen, press Down, Up, Left, Right, Up, Up, Start.
Add skill points:
At the team management screen, press Up, Up, Left, Right, Left, Right, Down, Up, Start.
While visiting the store, press Up, Up, Up, Down, Right, Right, Start.
The following party member combinations, provide each of those characters with the bonus listed:
Wolverine, Nightcrawler, Sunfire and Colossus activates 'New X-Men'. This provides an additional +15% of their maximum health.
Magneto, Juggernaut, Scarlet Witch and Toad activates 'Brotherhood of Evil'. This provides an additional +5% experience.
Jean Grey, Rogue, Storm and Scarlet Witch activates 'Femme Fatale'. This converts 5% of the damage you inflict into health.
Wolverine, Colossus, Juggernaut and Rogue activates 'Bruiser Brigade'. This gives a character +20 energy if their attack knocks their target down.
Change all the characters costumes to their original to activate 'Age of Apocalypse', which gives +100% to your attack rating.
Iceman is the strongest character in the game. If you boost him correctly, he can kill most of his opponents with just a single hit on melee attack. Distribute his Status Points wisely, developing more on his Focus and Speed. At his Projectiles Mutant Powers, concentrate on his Cold Crush, and a little in Freeze Beam and Ice Slide. Do not spend Skills Points in Boost Mutant Powers, as they are useless. Also, if the rest of this is done correctly, Iceman will grow strong enough to easily fight alone. Spend the maximum you can in his Passive Skills, particularly in Ice Combat and Cold Mastery. Get the Danger Room Disk: Challenge - Iceman, and get and equip his Signature Unique Item, Cryogenic Booster. That brings a very good trait, Double Cold Damage. As for other equipment, put some that give bonus to Damage (not Energy Damage, Electric Damage, or Radiation Damage). If done correctly, Iceman can hit easily his enemies (because of the high Speed), hit lots of enemies with the Cold Crush Projectile Mutant Power, and will inflict lots of damage. For example, you can do 500 and even more damage with melee attack, depending on your level, because of the Passive Skills, Ice Combat, Cold Mastery, and the Cryogenic Booster Signature Unique Item.
Once your characters get to about level 30, use Sunfire, Bishop, Toad, and Gambit as your team. The idea is to pump up Gambit as much as possible. Put as much of the stats as possible into each ability as follows: Sunfire = Flaming Fury, Bishop = Energy Fury, Toad = Secretion, Gambit = Energy Form. Also, put an extra 6 or 7 stats into each characters Mutant Mastery so that they will recover EP faster. During the game, activate all the abilities listed above and switch to Gambit. He will be able to run very fast and be super strong. Eventually he will have +200% movement, +400% or more attack and many of damage and defense bonuses. Also, because they regain their EP fast, you can reuse the abilities as soon as the affects wear off.