Enter "ERNESTO" as a profile name for invincibility. Additionally, while playing any mission in Single Player mode, press Select to complete the mission with a "Gold" rank. Pressing Select in a Challenge match will allow you to pass one part of that match. On certain levels and challenges after obtaining a "Bronze" or higher, "Silver" or higher, or "Gold" rank, you will unlock more playable characters and maps in Multiplayer mode. If you do this through the entire game, you will unlock everything.
Chili Con Carnage