Unlock Suits
Successfully complete the game under the Easy difficulty setting to unlock all suits, including Titanium Man.
Alternately, successfully complete the indicated mission to unlock the corresponding suit:
Classic - Beat the "One Man Army vs. Mercs" Challenge.
Classic Mark I - Beat the "One Man Army vs. AIM" Challenge.
Extremis - Beat the "One Man Army vs. Maggia" Challenge.
Hulkbuster - Beat the "One Man Army vs. AIM-X" Challenge.
Mark II - Beat the "One Man Army vs. Ten Rings" Challenge.
Mark III - Unlocked by Default.
Ultimate Suit - Finish story mode.
Titanium Man - Finish game on any difficulty setting.