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 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.
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.
One possible plot could be that Danny, through some sort of interdimensional portal accident, ends up in the Star Wars Rebels universe. He then uses his ghost powers to help the Rebels fight the Empire. Maybe his intangibility could be used to sneak past Imperial security or his ecto - blasts could be a new weapon against stormtroopers.
First, do your research on both universes. Know the characters, the technology, and the lore. For example, in Halo, understand how the Covenant works, and in Star Wars Rebels, know about the Empire and the rebels' fight. Then, create an interesting premise for the crossover. Maybe a shared threat or a scientific experiment gone wrong.
One idea could be that the OC is a new student in town. The OC has some unique powers that are a mystery even to themselves. Danny and Star notice the OC acting strangely and decide to investigate. Danny, being half - ghost, senses something different about the OC. Star, with her bubbly personality, tries to befriend the OC first. As they get closer, they discover that the OC's powers are linked to an ancient ghostly artifact that Danny has been researching. Together, they embark on a journey to figure out the origin of the OC's powers and protect the town from the potential threats that come with the artifact.
Sabezra fanfiction adds a lot to the fandom. It allows fans to explore the relationship between Sabine and Ezra in ways that the show might not have fully. For example, it can give more in - depth looks at their feelings for each other.
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.
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.
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.