6. The Injustice Syndicate
For every superhero, there is an alternate, evil version. The same is true for teams and in 2009's Batman: The Brave and the Bold episode, "Deep Cover For Batman," an alternate version of the Injustice League and Crime Syndicate are merged into a single, new group.
The Injustice Syndicate consisted of Owlman, the evil version of Batman, Blue Bowman who was Green Arrow's counterpart, Scarlet Scarab, and Silver Cyclone who were the Blue Beetle and Red Tornado's alternates respectively.
In the episode, Batman manages to travel to their evil dimension where he posed as Owlman in an attempt to learn the group's villainous plot. After infiltrating their ranks, he learns of their plan to destroy other universes, which is something Batman takes rather seriously.
Using his skills, Batman confronts and manages to defeat the Injustice Syndicate, saving the day once more all by himself. Who needs the rest of the Justice League when you're Batman?