Continue on to Act 2 without acquiring three Mutation bars in Act 1 for a certain character. Acquire at least two Mutation bars in Act 2 then go back to an Act 1 level and complete it on a higher difficulty for a 100% level completion. You will be given a Mutation bar, but you will not be allowed to add it because you can only add three bars to each character in Act 1. The game will not let you past this screen or regress any of the bars. You will have to restart the game.
Comic alternate costume
Collect all Sentinal Techs with a character to unlock his or her alternate comic costume.
Danger Rooms
You can unlock eight danger room missions. You must get all the Sentinel files and Weapon X files with all the character.
Finding Tech Pieces
To save time and frustration, run through the level on novice to find all six Tech Pieces, then distribute mutation and save the game. Go back on the higher levels to gain the missing mutations, without worrying about racing around trying to find the pieces (especially on timed missions).
Nightcrawler Danger Room
At the Cerebro Files Menu Screen, enter UP, UP, DOWN, DOWN, LEFT, RIGHT, LEFT, RIGHT.
Street alternate costume
Collect all Weapon X files with a character to unlock his or her alternate street costume.
Unlimited Health for Wolverine, Night Crawler, and Ice Man
When playing your mission, press start. Then hold all four buttons(L1,L2,R1,R2)and press up, up, left, right, up. Push start to get back in your mission. You should have unlimited health after that.
Unlock Danger Room Missions
There are eight danger room missions. You unlock the first three as you play through the game. To unlock the other six danger room missions, you must collect all Sentinel files and Weapon X files with each character.
Wolverine's Danger Room
Go to Cerebro and enter DOWN,DOWN,UP,UP,RIGHT,LEFT,RIGHT,LEFT.
X-Men: The Official Game Cheats Danger Room Unlocks
At the Cerebro Files menu, input the associated code to unlock stuff.