"Clash of the Titans" for the Microsoft Xbox 360 and Sony PlayStation 3 is based off the 2010 "Clash of the Titans" film. There is a co-op mode that allows two players to simultaneously play the game. The co-op mode is not unlocked at the beginning of the game, however, because you must unlock it during the single player mode.
Start a single player game and complete chapter two. To complete chapter two, you must beat Draco. Dodge his attacks, and then press "Y" on the Xbox 360 controller or "Triangle" on the PS3 controller to attack him.
Play the third chapter. A secondary character follows you.
Press the "Start" button on the second controller to control the secondary character.
You cannot select who the secondary character is and it will change during different chapters.