Meet Lydia, an average woman, going through a divorce, trying to get a loan application postmarked in time so she doesn't lose her home, thus losing custody of her kid, but it's currently 4:57, and there's a lady with about a billion different sized packages, taking up all the time... Then Superman and Batman come crashing through the post office, causing everyone, including the workers to scatter... So when the spores take over, and Lydia enters the game, her anger towards Superman destroying any chance she had at keeping her life normal is used towards controlling Batman to beat the shit out of Superman.
Turns out not everyone loves Superman, many believe he doesn't do enough, or overlooks some problems, as it seems like he can be everywhere in the world at once, but realistically can't, so some problems are going to fly by him, thus why it's so easy for people to turn on him, using Batman as their avatar.
Superman eventually gets tired of this, and tries to destroy Mongul's satellites, but he 1. can't and 2. it would kill Batman. So Superman comes up with a plan, allowing Batman to "beat him" in the game, which in turn, allows him to become part of the game, utilizing and acknowledging the trope that everyone (especially playing the game) knows, after heroes fight, they team up to fight the bad guy.
And they do, all the games players take over Batman and Superman to fight Mongul, eventually defeating the space tyrant. 12 hours later, Gotham is in cleanup mode, Toymaster has reverse engineered the nanobots on Batman, and Lydia is still without a loan... That is until Clark Kent shows up to interview her about the loan program she's been accepted into. Lydia doesn't believe it, but somehow, it turns out her application got in on time.
Elsewhere at the Fortress of Solitude, it's revealed that Mongul is now in the Phantom Zone, but Batman still isn't pleased with what happened, believing Superman's plan was too risky. Superman tells Batman to relax for once, and enjoy the victory. Batman eventually agrees to, but tells Superman he's not ignorant to how those games usually work, how once you think you beat the boss, the real one shows up later... in the Batman/Superman annual scheduled for later this month!