4. It Is impossible For Them To Rehash The Plot Of The Original
The unforgivable sin of any sequel is attempting to make money off the same movie twice. Disney itself made quite a killing in the direct-to-video market with this kind of sequel before Pixar came along (fun fact, Toy Story 2 was originally going to be direct-to-video before the Disney producers read the script and realized it was actually good) The fortunate thing about the way the first Incredibles was structured is that this approach would be virtually impossible. The climax of the first Incredibles is littered with self-aware teases at a possible sequel, but every one of them is closed up with an obsessive dedication to not leave any open ends. Even the closing moments, wherein a new Villain steps up to find the titular heroes, are handled more as a punchline than anything else. The Incredibles wasn't made to start a franchise, which is why it works so well - following this pattern, the sequel won't be made to "just be a sequel to The Incredibles".
Self-evidently a man who writes for the Internet, Robert also writes films, plays, teleplays, and short stories when he's not working on a movie set somewhere. He lives somewhere behind the Hollywood sign.