Fan Casting Justice League

We join the bigger world of superheroism as we find ourselves with a series of individuals who have been regularly teaming up to fight crime for some time now, but they're not a team. Not yet. They barely even know each other. They team up simply because it's easier. Less of an actual team-up, and more just fighting the same criminals at the same time. Then several super-powered individuals (The Crime Syndicate), eerily seemingly alike several of our heroes, are transported to Earth from another universe, and as each one of them are confronted by Earth's heroes, battles ensue. After the "Crime Syndicate" members get away, the heroes group and recollect themselves. As they struggle to stop the "Crime Syndicate's" havoc on Earth, they realize that they have to fight together, actually together, to stop the threat. They need to cooperate; they need to trust each other. And they eventually do. The heroes eventually learn that the transported meta-humans' Earth was invaded by an evil entity who killed all the other heroes of their world, which made the "Crime Syndicate" decide to travel to another Earth, and claim that one as their own, inadvertently becoming the very thing they were trying to escape, and our heroes help the Syndicate reclaim their Earth from the evil entity Amazo. The heroes return to their Earth a team, hailed by the public. Before the credits roll, we see the officially formed Justice League ready to defend the Earth from the intergalactic conqueror, Starro.