Complex sentence: Upon his return, he and his allies, along with Gotham's villains who felt neglected by Joker, zap the other villains back into the Phantom Zone, but the bombs detonate, causing an earthquake that splits the city in half.
Split into simpler sentences: Upon his return, he and his allies along with Gotham's villains who felt neglected by Joker, zap the other villains back into the Phantom Zone. Unfortunately, the bombs detonate causing an earthquake that splits the city in half.