One possible plot could be that in the future setting of Batman Beyond, an old threat from the Justice League's past resurfaces. Terry McGinnis as Batman Beyond teams up with the original Justice League members who have come out of retirement. They have to combine their old - school heroics with Terry's high - tech gadgets to defeat the villain.
Well, perhaps there's a new villain who has the ability to time - travel. This villain goes back in time and messes with the events that led to the formation of the Justice League. Batman Beyond somehow gets caught in the time - travel chaos and has to work with the young versions of the Justice League members to set things right. It could involve a lot of action scenes where Batman Beyond's advanced suit gives them an edge in battles, but also shows how the core values of the Justice League still hold strong even across different timelines.
Well, it could be about the Justice League traveling to the future where Batman Beyond operates. Maybe they need his help to fight a new threat that has some connection to their past villains. For example, a villain from the Justice League's past could have somehow influenced events in the future and they need Batman Beyond's knowledge of the future tech and his unique fighting style to stop it.
A good main villain could be Brother Eye. It's a powerful and menacing artificial intelligence. In a crossover, it could have evolved in the future to be even more dangerous. It could pose a threat to both the future world of Batman Beyond and the past era of the Justice League, forcing them to team up to take it down.
One idea could be a time - traveling adventure. Batman Beyond gets sent back in time to the era of the original Justice League. He has to team up with them to stop a threat that was once thought defeated but has returned in a new form. The contrast between the high - tech world of Batman Beyond and the more classic superhero settings of the original Justice League would create interesting dynamics.
Well, it could be about Batman initially being hesitant to fully join the Justice League. Maybe he has trust issues with some of the members at first. Then, he gradually starts to work with them on a big threat that requires all their skills combined, like an alien invasion or a powerful super - villain that's too much for any one hero to handle alone.
Well, it could be that Batman gets caught in a powerful explosion during a fight against a super - powered foe. His suit is damaged, and he suffers from severe burns and internal injuries. The Justice League is then faced with the challenge of getting him medical help while also preventing the villain from achieving their evil goals. They might have to split up, with some members protecting Batman and others going after the bad guy.
There's also 'The Dark Knight of the Future in the League'. This fanfiction focuses on Batman Beyond's unique perspective within the Justice League. It shows how his different set of skills, being more in tune with the future tech, can be both an asset and a source of conflict. It's not too long but packs a punch in terms of character development and action scenes.
Ink could be a great main antagonist. He has the power to manipulate shadows and could use this ability to create chaos in Gotham and beyond. He might target the Justice League and Batman Beyond because they represent order and he wants to spread his own brand of darkness.
One popular storyline could be a time - travel adventure. Imagine Batman Beyond getting accidentally sent back in time to the era of the original Justice League. He has to team up with the younger versions of the heroes to stop a threat that could change the future. For example, a villain from his time could have followed him back and is now trying to rewrite history to gain ultimate power.
A cool plot could be that there is a rift in the multiverse that is causing chaos. Batman Beyond discovers it first and tries to get the Justice League's help. Along the way, they encounter alternate versions of themselves and have to work together to close the rift while also dealing with the differences and similarities between their various selves.
Well, one possible plot could be that the Justice League and the Marvel heroes are brought together by a powerful cosmic entity to fight a common enemy that threatens both their universes. Maybe Thanos teams up with Darkseid, and the combined forces of Superman, Batman, Captain America, and Iron Man have to figure out how to work together to stop them.