Cheat mode - At the main menu, press L(2), R(2), B(2), Y(2), X(2). There is no confirmation message. Start a game, then pause and enter the options screen. The "Cheats" option will be available at the options menu.
Destroying armored vehicle or tanks - Use Jones to run up to the vehicle or tank. Lay an anti-tank mine next to it, in turn sacrificing jones Temporarily to take out the vehicle or tank.
Extreme mode - Successfully complete the game on the hard difficulty setting to unlock the extreme difficulty setting.
Healing falling teammates - If one of your teammates falls to the ground, throw a smoke grenade near him. Then, get your health packet out and heal him.