The fanfiction could begin with the Justice League investigating strange paranormal activities. They discover Danny Phantom in the middle of a battle with some powerful ghosts. Danny is initially hesitant to join the League as he has his own problems in Amity Park. However, as he realizes the scale of the threats the League faces, he decides to join. He could teach the League members about the ghost zone and its rules. In return, they could help him better control his powers and protect his town from any spill - over threats from the League's villains.
One possible plot could be that Danny Phantom's ghostly abilities are detected by the Justice League. They initially view him as a threat but then realize he can be an asset. Danny could help them with foes that have intangible or otherworldly powers. For example, against an enemy that can phase through walls or possess people, Danny's experience dealing with ghosts would come in handy.
Well, he could bring his unique ghost powers to the team. His intangibility and invisibility would be great for stealth missions. And his ghost ray could be a powerful offensive weapon. Maybe he'd also have some funny interactions with the more serious Justice League members like Batman.
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.
Well, it could be about Danny's powers being a great asset to the Young Justice team. Maybe he helps them with his ghostly abilities like intangibility and invisibility during a mission where they need to infiltrate a highly - guarded enemy base. His unique perspective as a half - ghost could also offer new strategies to the team.
One possible plot could be that Danny Phantom is facing a threat in his own dimension that is beyond his control. He decides to call the Justice League for help. Maybe he first has to figure out a way to contact them across dimensions. Once he does, the Justice League initially doubts his claims but as they start to investigate, they realize the severity of the situation and they all work together to fight the new and strange enemies from Danny's world.
In this fanfiction, perhaps Danny Phantom discovers a plot against the Justice League early on. He then uses his invisibility and intangibility to gather information. His ability to fly and super strength (in his ghost form) would be crucial in battles against the villains targeting the League. For example, if the villains had some sort of kryptonite - like weapon against Superman, Danny could use his powers to either disable the weapon or protect Superman until they find a way to neutralize it.
In such a crossover, Danny could team up with Superman. Danny's ghost powers would be really interesting combined with Superman's super strength. Maybe they'd fight a common enemy that has powers related to both the supernatural and advanced technology.
Well, Danny could use his ghostly powers to play all sorts of tricks on the Justice League members. Maybe he turns Superman invisible for a while just to see his confusion. Or he makes Batman's utility belt float away when he's in the middle of a fight.
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.
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.
One common theme is the clash of two different worlds. Danny comes from a world where ghosts are a big part of his life, and the Justice League is from a more traditional superhero world. So there's often a theme of how they deal with each other's differences.