In a fanfiction, Danny Phantom might be able to defeat the Justice League by exploiting their weaknesses. For instance, Green Lantern's constructs are based on willpower. Danny could use his ghostly wails to disrupt that willpower. Also, his ability to create ice with his ghost powers could be a problem for Flash, as it could slow him down. Danny could also play mind games with Martian Manhunter, given his own experiences with different - minded foes in his own world.
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.
Danny Phantom has a lot of tricks up his sleeve. He could use his intangibility and invisibility to get close to the members of the Justice League without being detected. Once close enough, he could use his ecto - blasts to incapacitate them one by one. His ability to transform into different forms, like his more powerful ghost forms, could give him the upper hand in a battle. He might also be able to manipulate the energy around him in a way that the Justice League has never encountered before, which could lead to their defeat in the fanfiction.
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.
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.
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 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, 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.
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.
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.
It would disrupt the normal dynamic. The Justice League is used to dealing with threats they can see and understand. Danny Phantom's ghostly nature means he can be unpredictable. His haunting could make the heroes more on edge and less trusting of their surroundings.
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.