A fun way would be to have Star Wars characters visit Amity Park. Han Solo and Chewbacca might find the whole concept of ghosts very strange. They could get involved in one of Danny's battles against his ghost enemies, adding their blaster - shooting skills to the fight.
The Sith Lords could be interested in Danny's powers. They might try to corrupt him or use his powers for their own evil purposes. Danny would have to resist their temptations, like how Jedi resist the dark side of the Force. And his friends from both worlds would help him in this struggle.
First, you need to research both universes well. Know the characters, their abilities, and the settings. For Danny Phantom, understand his ghost powers and the rules of the Ghost Zone. In Star Wars Rebels, be familiar with the different species, ships, and the power of the Force.
One idea could be to have Danny Phantom's powers in the Star Wars universe. For example, he could use his intangibility to sneak past stormtroopers or his ghostly energy blasts as a new type of weapon. Maybe he gets caught in a wormhole and ends up in a galaxy far, far away and has to find his way back home while getting involved in the Galactic Civil War.
One great fanfiction could be a crossover where Danny Phantom's powers are used in the Star Wars Rebels universe. Maybe Danny accidentally gets transported there and has to use his ghostly abilities to help the rebels. For example, his intangibility could be used to infiltrate Imperial bases unnoticed.
One idea could be that Danny Phantom somehow gets transported to the Star Wars universe. Maybe he uses his ghost powers to help the Jedi or the Rebels. For example, his intangibility could be useful in sneaking past enemy defenses.
Danny could be a new type of being in the Star Wars universe. He might be seen as a mysterious entity with his ghost - like powers. He could start off as an outsider, like Luke Skywalker was on Tatooine, but with his own set of abilities that make him both feared and respected. For instance, his invisibility could be a huge advantage in espionage - like missions.
The Covenant's energy weapons and their unique alien abilities could mix with the Star Wars technology and Force powers in various ways. The Grunts could be like the Ewoks in terms of being small but fierce when combined with the right support. The Elites' combat skills might be on par with some of the Star Wars bounty hunters, and together they could form an interesting team.
I'm not sure of specific ones directly from 'danny phantom tue fanfiction', but some general great Danny Phantom fanfictions often focus on Danny's growth as a hero. They might show him becoming more confident in his powers. Some also explore his relationships with other characters like Jazz, his sister. You can search on popular fanfiction websites and look for ones with high ratings and good reviews.
The characters can be integrated in various ways. Danny could befriend Hiccup as they both have a sense of being different from their peers. Danny is a half - ghost and Hiccup was initially seen as an outcast among the Vikings. They could share their experiences of not fitting in. Astrid could be curious about Danny's powers and train with him, learning new combat techniques that combine Viking fighting skills with Danny's ghostly moves.
Yes, there are quite a few. You can start by looking on fanfic platforms like Archive of Our Own. Some fanfics might combine the unique ghost - hunting elements of Danny Phantom with the epic space battles and Rebel - Empire dynamics of Star Wars Rebels in really creative ways.
Danny Phantom can go intangible and invisible, which would be really useful for sneaking up on enemies. Wonder Woman has her super strength and speed. So, Danny could use his invisibility to get close to an enemy unnoticed, and then Wonder Woman could quickly rush in with her super strength to take the enemy down. For example, if they were facing a group of powerful demons, Danny could scout ahead invisibly and then signal Wonder Woman to attack.