One idea could be that Danny and Jinx accidentally cross paths in a dimension where the laws of magic and the supernatural are all jumbled. Danny is trying to find his way back home and Jinx, initially seeing him as a threat, later realizes they can help each other. They team up to navigate through this strange dimension and along the way, they learn about each other's powers and develop an unlikely friendship.
A fanfiction could be set where Jinx is on the run from some magical authorities in her world and she stumbles into Danny's world. Danny finds her and at first is suspicious but then decides to help her hide. As they spend time together, Jinx starts to understand the concept of protecting the living from the dead in Danny's world and Danny learns about the complex magic politics in Jinx's world. Their friendship blossoms as they face challenges together, like when some of Jinx's pursuers cross over into Danny's world.
Maybe in a fanfiction, there's a villain who is causing chaos in both Danny's world and Jinx's world. They are both independently trying to stop this villain. Eventually, they discover that they are after the same bad guy. They combine their powers, with Danny's ghostly abilities and Jinx's magic, to take on the villain. Their different personalities, Danny's more heroic and Jinx's more chaotic - good, create an interesting dynamic as they work together.
A good crossover could be where Danny's ghost sense goes off when Jinx uses her magic for the first time near him. He thinks she's some kind of new ghostly threat. But as he approaches her, he realizes she's something different. They start off as enemies but as they learn more about each other's powers and motives, they become allies. For example, they might team up to stop a powerful entity that is trying to use both magic and the power of the ghosts for its own evil purposes.
One idea could be that Dash gets in trouble and Danny Phantom, instead of using his powers to embarrass him like he usually might, decides to help him secretly. This could lead to an unlikely friendship between them as Dash starts to suspect that there's something different about Danny but can't quite put his finger on it.
One idea could be that Danny and Sam have kids in the future and their kids inherit Danny's ghost powers. The story could focus on how they learn to control their powers while also dealing with normal kid stuff like school and making friends. It would be interesting to see how Sam, as a mom, guides them through this.
One idea could be that Danny gets an illness that affects his ghost powers. For example, he might start losing control over his intangibility or invisibility. This could lead to some really comical or dangerous situations. Another idea is that his friends try to find a cure for his strange ghost - related illness while also keeping it a secret from the town.
One idea could be exploring Danny's relationships in a different way. For example, how his friendship with Sam and Tucker might develop if they faced a new supernatural threat. Another could be a story where Danny discovers a new power and has to learn to control it while dealing with school and his ghost - fighting duties. And perhaps a fanfiction where Danny travels to an alternate dimension within the Danny Phantom universe.
A fanfiction could also explore a scenario where Peter Parker gets some ghostly powers similar to Danny's due to an experiment gone wrong. He then has to learn how to control these new powers while still being Spiderman. Danny could come to help him understand and master these powers.
Another possibility is a time - travel fanfiction. Danny and Dani accidentally travel back in time and have to figure out how to get back. Along the way, they meet younger versions of their friends and family and have to make sure they don't change the future too much. This could explore their relationship in a different setting and also show how Dani's powers might be different in the past.
One idea could be a story where Danny and Desiree's marriage is a way to break a curse. Maybe Desiree was cursed to grant wishes in a harmful way, and by marrying Danny, who has ghost powers, they find a way to reverse the curse. Their relationship could start as a reluctant alliance but grow into true love as they face various challenges together.
Another fanfiction could focus on a friendship developing between Danny and Shego. Shego initially sees Danny as a nuisance but gradually realizes his good intentions. They could start training together, with Danny teaching Shego some ghost - fighting techniques and Shego showing Danny some of her martial arts skills.
One idea could be that the Joker somehow finds his way into the Danny Phantom universe. Maybe he teams up with one of Danny's villains, like Vlad, thinking they can cause more chaos together. They could plan to use Danny's ghost powers for some really wild and dangerous stunts across both the human and ghost worlds.