One possible plot could be that Danny and Ben meet when a powerful interdimensional villain is causing chaos in both their universes. They initially misunderstand each other and get into a small fight. But then they realize they need to work together. Danny could use his ghost powers to phase through objects and surprise the enemy, while Ben could use his various alien forms to combat the villain's different attacks. For example, using Heatblast to counter a cold - based attack from the villain.
A cool plot might be that a group of alien ghosts are invading Earth. Danny, as the local ghost hero, starts to fight them off. But these alien ghosts have some strange powers that Danny has never seen before. Meanwhile, Ben is on a road trip and his Omnitrix starts acting up because of the alien - ghost energy. He tracks it down to Danny's town. At first, Danny is a bit suspicious of Ben, but when they see the power of the alien ghosts together, they team up. Ben uses XLR8 to quickly move around and gather information about the ghosts' weaknesses, and Danny uses his ghostly wail when they finally face the big boss of the alien ghosts.
Maybe in this crossover, some Pokemon are accidentally sent to Danny's world. Danny has to protect the Pokemon from being captured by the Guys in White while also trying to find a way to send them back. Meanwhile, a certain Pokemon, like Gengar, forms a special bond with Danny because of their shared ghostly nature.
One interesting plot could be that a powerful ghostly villain from Danny's world somehow crosses over into the Young Justice universe. This villain starts causing chaos and Danny has to team up with the Young Justice heroes to stop it. Along the way, they learn about each other's powers and worlds.
Well, a cool plot might be that the Ice Age animals discover a strange, glowing object which turns out to be a device from Danny Phantom's world. This device starts causing strange things to happen in the Ice Age, like creating areas of anti - gravity or making the ice melt in odd patterns. Danny Phantom shows up to retrieve the device and ends up teaching the Ice Age animals about his world of ghosts and technology while they all work together to fix the problems the device has caused.
Well, imagine if there was a device in the Danny Phantom universe that malfunctioned and created a portal to the Harry Potter world. Danny ends up at Hogwarts during the Triwizard Tournament. He gets involved in the tasks because his powers are seen as an advantage. He might team up with Harry and use his intangibility to pass through obstacles in the maze during the third task. At the same time, he could teach Harry some of his skills, like how to quickly phase through walls to avoid danger.
A Danny Phantom and Ben 10 crossover fanfiction would be full of action and adventure. The two characters have very different power sets. Danny has his unique ghost powers such as flight, invisibility, and ecto - blasts. Ben, on the other hand, can transform into a variety of aliens with different abilities like Four Arms' great strength or XLR8's super speed. In the fanfiction, they could be brought together by a common enemy that is threatening both the human world and the ghost zone. They would have to learn to work together, with Danny using his knowledge of the supernatural world and Ben using his combat experience from different alien forms. Their combined efforts would make for a thrilling story as they face challenges that neither could overcome alone.
Well, the plot could start with a scientific experiment gone wrong in both their universes simultaneously. This creates a rift that pulls Danny into the Flash's world. There, they find out that a common enemy is trying to use the chaos to gain power. This enemy is using a device that can steal powers. Danny and the Flash team up. Danny's ability to go invisible and intangible helps them in stealth missions, while the Flash's super speed allows them to quickly reach different locations. In the end, they manage to defeat the enemy and Danny finds a way back to his own universe.
In this fanfiction, it could be that Danny Phantom meets a Danny Phantom from a parallel fan - made story. At first, they don't trust each other. But as they learn more about each other's worlds, they realize that there are some common elements that are being threatened. It could be that a powerful ghost is trying to rewrite all the fanfic universes related to Danny Phantom. So, they must combine their strengths and knowledge to stop this from happening.
Maybe there's a villain who has the ability to cross between the dimensions of Danny's world and the Young Justice world. Danny and the Young Justice team have to combine their efforts to stop this villain. Danny could teach them about dealing with supernatural threats, while they could show him how to work better in a team setting in a more traditional superhero sense.
It could be an evil scientist who has found a way to combine ghost and alien technology. He wants to use this to take over both the human world and the ghost zone.
Maybe Danny gets transported to a different dimension where there is a harem - like society. The local girls there are intrigued by his ghost powers and his heroic nature. They start following him around, and he has to figure out how to deal with their attention while also trying to find a way back home. Some of the girls might be from different species, which could add more interesting elements to the story, like different cultural norms regarding relationships.