Well, consider a crossover where all the Justice League members are pitted against a group of supervillains who have formed an alliance stronger than ever before. Each hero has to use their powers in a new and creative way. For example, Superman might have to use his heat vision in a more precise and surgical way to disable the high - tech weapons of the villains. Batman has to rely on his detective skills more than ever to figure out the villains' master plan. And the other heroes like Green Arrow, Hawkman, etc. also have to step up and contribute in ways that highlight their individual strengths.
A cool plot for dc super heroes crossover fanfiction could involve Wonder Woman and Aquaman. Maybe there's a threat that endangers both Themyscira and Atlantis. They must combine their unique skills, like Wonder Woman's combat abilities and Aquaman's control over the sea, to save their respective homes. Also, a Martian Manhunter and Cyborg crossover could be interesting. The Martian Manhunter's shape - shifting and telepathy, along with Cyborg's technological prowess, could be used to stop a cyber - psychic threat.