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.
Obviously, Danny Phantom is one of the main characters as the title implies he's the one doing the pranking. And then, members of the Justice League like Superman, Batman, Wonder Woman, Flash, etc. would be the ones being pranked.
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.
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.
I think there's no clear - cut winner in a 'danny phantom vs justice league' fanfiction. Danny Phantom is a powerful ghost - hero in his own right. He has unique powers that the Justice League may not be familiar with at first. But the Justice League is a team of some of the most powerful heroes in the DC universe. If the story is written in a way that Danny has some sort of ace up his sleeve, like a new power or a powerful ghost artifact, he could potentially defeat the Justice League. On the other hand, if the Justice League is well - prepared and uses their combined skills effectively, they could overpower Danny.
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.
Obviously, the main character would be Danny Phantom himself, but in two different forms or versions. One would be the original Danny Phantom from the canon source, and the other would be a version created by the fanfiction. There might also be his friends like Sam and Tucker who could play important roles in helping the two Dannys understand each other and deal with any issues that arise from their meeting.
Danny Phantom himself is obviously very popular as he is the main character from his own series. His ghost - fighting abilities and his dual identity make him an interesting addition to the Justice League universe.
Lex Luthor could be a likely villain. He's always devising plans to take down the Justice League, and this time he might have come up with a scheme that almost succeeds, until Batman steps in. For instance, he could create a super - weapon that targets the unique powers of each Justice League member.
Obviously, Danny Phantom and Ember would be the main characters. Danny is the half - ghost protagonist who is being raised by Ember. Ember, a ghost with music - related powers, would play the role of his caretaker or mentor in this fanfiction.
The characters interact in various ways. Danny could be called upon by the Justice League to deal with a particular threat that has a connection to the Ghost Zone. He would then have to work alongside heroes like Superman or Batman. Superman might be curious about Danny's powers, as they are so different from his own. Batman, of course, would be analyzing Danny's abilities and trying to find any potential weaknesses. Danny's enemies from his own series could also be involved, and the Justice League would have to learn how to deal with these new types of foes.