To do this code, start off with doing a ,ission and once you start, dont do anything. Press Start and then press L, R, Down, Down. If you did this right, then you should go back to playing. Don't do anything and then for a few seconds, a screen will pop up saying you completed the mission. This will help for those people who can't pass a mission.
Lone Wolf mode
Successfully complete all the missions to unlock Lone Wolf mode. You can only control one character in this mode.