The Phantom Troupe could form an uneasy alliance with some of the more morally grey members of the Justice League, like Catwoman or Lobo. They might team up to take down a common enemy that the League can't deal with using their usual methods because of legal or moral constraints.
Imagine a scenario where the Phantom Troupe uses their skills to infiltrate the Justice League's headquarters. They could steal some of the League's advanced technology and use it to enhance their own powers. This would force the League to go on a hunt to get their stuff back and stop the Troupe from causing more harm. It would be a story full of action, mystery, and strategy as both sides try to outwit each other.
One possible fanfiction could involve the Phantom Troupe's unique abilities clashing with the superpowers of the Justice League members. For example, Chrollo's nen ability to steal other's abilities might be a huge threat to the League. Maybe he targets Superman and tries to steal his super strength. This could lead to an epic battle where the League has to figure out how to counter the Troupe's devious tactics.
I think Superman would be the most likely. Superman is known for his kind heart and open - mindedness. He would probably see Danny as a young hero in need of some guidance and friendship. He wouldn't be too quick to judge Danny based on his ghostly appearance or powers.
I think it could be Superman. Superman is all about truth and justice and he would likely see the good in Danny. Also, they both have super strength in a way. Danny has his ghostly strength and Superman has his Kryptonian strength. They could bond over protecting the innocent.
One idea could be that Robin is on a solo mission when he accidentally stumbles into a Justice League operation. He then has to prove himself to the League members and ends up joining them for that particular mission. Another could be Robin discovers a secret about a member of the Justice League that puts him in a difficult position of whether to expose it or not.
One idea could be Sonic's speed causing chaos among the Justice League at first. For example, he might accidentally disrupt Batman's plans during a Gotham operation. Another could be Sonic teaming up with The Flash to outrun a common enemy that is threatening both their worlds. Maybe they have a friendly race while also trying to lead the bad guy into a trap.
One idea could be that the Flash from Arrowverse accidentally runs into a different dimension where he meets the Justice League. He then has to team up with them to stop a powerful villain that is threatening both his world and the Justice League's world.
In such a fanfiction, there might be a big threat that requires both teams to combine their skills. The Flash could race with Kid Flash and share some speed - related tips. And Wonder Woman could train the female members of Young Justice in combat.
Brucie in this fanfiction could be someone who has been living on the fringes of society. He might be a street - smart person who has a deep understanding of the underbelly of the city. When the Justice League meets him, they realize that his knowledge can be useful in their fight against crime. He could also be a bit of an outcast, which makes his relationship with the super - heroes all the more interesting.
Danny could use his ghostly powers to disrupt the technology that some Justice League members rely on. For example, he could mess with Cyborg's systems. His ability to overshadow people might also be a key factor, allowing him to control some of the less - powerful members.
I'm not entirely sure as I haven't read this specific fanfiction. It could be about a disrupted or alternative version of a story where Danny Phantom interacts with the Justice League in some unexpected or 'broken' way.