Beat World 12 to unlock Extra Mode for the Forever Crossing mini game, a much faster and more difficult mode.
Successfully complete World 12.
After you beat the game. World 7 will now be available.World 7 is a faster and much harder version of World 1. Beating World 7 will unlock 8 and consecutively up to World 12 which are all harder versions of worlds 1 through 6.
Complete every stage making sure to not skip over any when the path branches off and beat the game. The question marks on the main menu will now say Challenge.
Successfully complete the game to unlock Worlds 7 through 12, which are harder versions of Worlds 1 through 6.