A set of 7 mission cards are required for each deck. Mission cards are used to venture each round. A player can venture 1, 2, or any number of missions for the current battle. If you choose to venture more than 2 mission cards per battle, you will incur a penalty. If you are successful in winning the battle, your ventured mission cards are moved to the completed pile. Consequently, if you lose the battle, your venture cards are moved to the lost pile. When all 7 mission cards are moved to the completed pile, you win the game.
Below are a few pics of various mission cards (Marvel, Image, and JLA).