9. Return to a Sub-Plot Much More Important Than the Rest of the Movie
Perpetrator: G.I. Joe: The Rise of Cobra Something awesome happens in the first G.I. Joe film. The bad guys are able to make a "duplicate" of the President of the United States and get him to take the place of the real thing. The possibilities for this are practically limitless. It's something that could really drive the narrative of the current movie to something much bigger and better than it already is. Except that they only return to it right before we get smacked with the credits. The movie finds its climax in something else and comes to a completeness without ever trailing back to the aforementioned scenario as something foreboding that can be taken care of in one viewing. It's a means of setting up the plot in the first one so time doesn't have to be wasted in the sequel to explain what's what. The "second try" can go for a single-line, tell-not-show exposition if it wants to, which is awfully convenient, wouldn't you say?