At the episode selection screen after starting a new game, press X, Y2, X2, Y, X, Y. Alternately, successfully complete the Light Campaign.
Pause game play, then press X, Y, X, X, Y, Y, X, Y, X, X, Y, Y to unlock "God Mode" and "Complete Mission" options at the pause menu.
You unlock the Stone Gnome once you beat the dark campaign.
Play as Earth Golem
Successfully complete the Light Campaign to unlock the Earth Golem as a playable character. He cannot do much more than attack, and he cannot be equipped with any weapons or armor, but he is very powerful.
Enemies in the light campaign die after five to ten seconds or more if they are standing in water on the beach. If you can lure enemies into the water you can kill them without getting hurt. Works on goblins may work on large enemies.
Get ALL of the gold in the Dark Campaign
Unlock 9320 Battle Droid
Get ALL of the gold in the Light Campaign