In a different scenario, Danny could be mistaken for a new type of Faunus in the RWBY world. His powers would be a mystery to everyone at first. As he tries to figure out how to get back home, he starts to train with the students at Beacon Academy. His unique abilities would inspire new combat techniques among the students.
One idea could be that Danny, with his ghost powers, ends up in the RWBY universe. He could team up with Team RWBY to fight off Grimm that are being influenced by some sort of ghostly energy. His intangibility and flight would be really useful in battles.
One idea could be that Danny's ghost powers somehow interact with the Cybertronian technology in the Transformers Prime universe. Maybe his ectoplasmic energy can power up or disrupt certain Cybertronian devices. For example, he could accidentally short - circuit a Decepticon weapon while trying to use his powers to protect a human from an attack.
I like the idea of a Danny Phantom and Ben 10 crossover. Ben has the Omnitrix which gives him access to different alien forms, and Danny has his ghost powers. They could either be rivals at first, each thinking their powers are better, or they could quickly team up to face a threat that requires both their unique abilities. It would be a fun clash of two very different power - based universes.
Maybe in this fanfiction, the world of Danny Phantom is being invaded by demons. The exorcist arrives in Amity Park to help. Danny initially doubts the exorcist's methods but soon realizes they can be a powerful ally. They learn from each other's techniques, like Danny teaching the exorcist about ectoplasm and the exorcist showing Danny ancient exorcism spells.
One idea could be that Danny, as a half - ghost, has to prove himself to the Ghost King. Maybe there's a tournament in the Ghost Zone where Danny enters to show his worth. This could lead to some epic battles and alliances with other ghosts.
For the crossover, a good plot could be that a new type of ghost appears that is immune to Danny's ghostly powers. The Ghost Hunt team, which has encountered a similar situation before, offers their expertise. They introduce Danny to a special type of ectoplasm - based weapon that can harm this new ghost. Danny then teaches them some of his combat moves as a half - ghost to better fight the ghost.
One idea could be that the Totally Spies are sent on a mission to investigate some strange paranormal activities. They then discover Danny Phantom's world and team up with him to stop an evil force that is using both magic and technology to take over the world. Danny could teach them about the Ghost Zone and they could share their spy skills with Danny.
One idea could be Danny Phantom teaming up with characters from other Nickelodeon shows to fight a common supernatural threat. For example, he could join forces with the Teenage Mutant Ninja Turtles. They could use their unique skills, Danny with his ghost powers and the Turtles with their ninja skills, to take on a powerful ghost - mutant hybrid enemy.
One idea could be to explore how Danny's ghost powers interact with the dark and tortured world of 'The Suffering'. Maybe he gets trapped in that nightmarish realm and has to use his unique abilities to survive and find a way out. Another idea is to have some of the tortured souls from 'The Suffering' cross over into Danny's world and how he deals with them while keeping his identity as a half - ghost a secret.
One idea could be that Danny's ghost powers somehow interact with the dragons in HTTYD. For example, his intangibility might make him able to pass through dragon fire without getting burned, and this could be a crucial skill when dealing with a new, more dangerous breed of dragons. Another idea is that Danny gets transported to the world of HTTYD and has to use his ghostly abilities to fit in and help the Vikings. Maybe he can use his flight ability to race against the dragons, which would be an exciting plot point.
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.