You have been locked up by The Empire for your rebellious actions. You are a key member of the rebellion that is conspiring to assassinate the emperor and will not be stopped by petty concrete walls. Time to escape. Challenge mode reduces the number of power ups you receive, moves and/or replaces certain enemies, and makes enemies much more effective at spotting and shooting you. The changes are subtle but make the game hard enough for even the most seasoned of shooter players to be challenged. If this is too hard for you, then try the normal difficulty: http://www.sploder.com/games/members/ravicale/play/imprisoned/
