As weird as this may sound, just try to understand it: Have something happen where a large majority of the good and bad people actually get converted to a 3rd faction, which is basically super evil. This faction is a threat to both the rebels and the dark side, as they will wipe out essentially everything. The dark side winds up TEAMING up with the rebels to defeat the 3rd faction, and in the final movie, you will have a final battle with 1 dark side person, 1 rebel teamed up against 1 or 2 faction people. They obviously destroy the faction people, but the dark side then persists to his normal routine, leading to the dark side guy backstabbing the rebel!
Money can't buy happiness. Just video games, which make me happy.







