In Avengers: Endgame, the surviving members of the team must band together and find a way to reverse the damage done to the universe by Thanos -- or at least get revenge on the Mad Titan. That's already one epic logline that promises drama and action, and fan theories have risen up to try and plug the various holes. People have pitched everything from time travel to Ant-Man jumping up Thanos' butt, but whatever it ends up being, it will be absolutely wild.