During play, pause the game and enter X, Y, X, X, Y, Y, X, Y, X, X, Y, Y to access the cheats menu. From here you can toggle God Mode or Complete Mission.
Play Dark Side:
Start a new game. At the episode select screen enter X, Y, Y, X, X, Y, X, Y to unlock the Dark Side Campaign.
Unlock the 9320 Battle Drone:
Collect all the gold in the Light Campaign to unlock the 9320 Battle Drone.
Unlock the Earth Golem:
Beat the Light Camplaign to unlock the Earth Golem.
Collect all the gold in the Dark Campaign to unlock Fetica.
Unlock the Stone Gnome:
Beat the Dark Camplaign to unlock the Stone Gnome.
Thanks to Revolution readers The Blade, Doug Brown, Micheal Little, Paolo Augello, and Richard Heath!