Unlock Cardboard Characters
Beat TimeSpliters 2 on Easy to open flat/cardboard characters.
Unlock Characters in Arcade Mode
Get a Gold medal in "Adios Amigos" (in the Arcade Mode) and you'll open playable characters Hector Babasco and Lean Molly.
Unlock Characters in Story Mode
Beat the coresponding levels on Medium difficulty to unlock the following secret playable characters:
Unlock Rotating Heads Cheat
Complete "Pane in the Neck" and get Silver (in Challenge Mode) to unlock the Rotating Heads cheat.
Unlock Streets Arcade Level
Complete TS2 on Easy to unlock the Streets arcade level.