X-Men: The Official Game
Hidden Item Guide
At the Cerebro Files menu, press Right(2), Left(2), Down, Up, Down, Up, Start to unlock the bonus Iceman Danger Room missions. -From: thomastodd
At the Cerebro Files menu, press Up(2), Down(2), Left, Right, Left, Right, Start to unlock the bonus Nightcrawler Danger Room missions.
At the Cerebro Files menu, press Down(2), Up(2), Right, Left, Right, Left, Start to unlock the bonus Wolverine Danger Room missions.
Successfully complete an Act with a character to unlock one of their Danger Room mission. Successfully complete all three Acts with a character to unlock all three of their bonus Danger Room missions.
Collect all Weapon X files with a character to unlock their street costume. Collect all Sentinal Techs with a character to unlock their comic costume.
To save time and frustration looking for Tech Pieces, go 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 get the missing mutations, without worrying about racing around trying to find the pieces (especially on timed missions).