Betrayal is definitely needed, I say. Not everyone should play fair, or even want to for that matter. They are there for something important to them, and that should be their goal. 

Would the coordinator of the game (I'm assuming this is the Devil) tell them all of the rules outright? If he were trying to just screw them over, he could hide some of the facts, such as they could die if their souls don't get back to them in a certain amount of time. He could only say like, keep these souls, they will be your key to salvation. At first everyone could think like, oh well we all have a chance to win. We need to work together to get to the final point, and when we do, we can all get our wishes. Then someone could drop a vial or something, just kill off a random side character that doesn't matter, and everyone freaks out. 

I'll think more on it while I'm at work, and I'll tell you if anymore possible ideas come to mind!