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.
In a 'danny phantom vs justice league' fanfiction, Danny could use his ghost powers to surprise the Justice League members. His intangibility and invisibility might give him an edge at first. Maybe he'd startle Superman by suddenly phasing through a wall. However, the Justice League has a vast array of powers and skills too. Batman could potentially figure out Danny's weaknesses with his detective skills. And Wonder Woman with her combat experience could pose a real threat to Danny in a face - to - face battle.
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, 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.
Danny Phantom is for sure the main character on the saving side. On the Justice League side, all the classic members would probably be there. Superman, being the symbol of hope and having super strength, heat vision etc. Batman, the Dark Knight with his gadgets and detective skills. Wonder Woman with her Lasso of Truth and superhuman strength. The Flash, who can move at incredible speeds. Green Lantern, who can create constructs with his power ring. And Martian Manhunter, with his shape - shifting and telepathic abilities. They all could be in danger and Danny would have to figure out how to save each of them based on their unique powers and vulnerabilities.
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 a Danny Phantom and Justice League crossover fanfic, Danny could team up with Superman. Maybe Danny uses his ghost powers to help Superman when he's facing a powerful ghost - like enemy that the Justice League can't handle with their normal tactics. It would be a really cool combination of the two universes.
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.
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.