One idea could be a crossover with 'Futurama'. The Simpsons characters could travel to the future and interact with Fry, Bender and the rest. Maybe Homer gets a job at Planet Express and causes all kinds of chaos with his clumsiness. Another could be a crossover with 'South Park'. The two sets of very different characters would create a really comical and chaotic situation. For example, Bart could get into a prank war with Cartman.
A great idea for 'the simpsons crossover fanfic' would be a crossover with 'SpongeBob SquarePants'. Imagine Homer getting a job at the Krusty Krab and causing all kinds of chaos. Bart could also become friends with SpongeBob and they get into mischief together. Additionally, a crossover with 'Scooby - Doo' would be exciting. The Simpsons could join the Mystery Inc. gang to solve a mystery in Springfield, like a haunted mansion that turns out to be a scheme by Mr. Burns to scare people away from a piece of land he wants to buy.
Well, a great Simpsons fanfiction concept might be centered around Mr. Burns getting amnesia and forgetting he's rich. He then starts living a normal life and has to learn about kindness and friendship from the other Springfield residents. Also, you could write a fanfic where Nelson actually has a soft side and befriends Lisa, and they have adventures together. And there could be a story where Krusty the Clown tries to retire but the town won't let him because he's such an important part of Springfield's culture.
One idea could be exploring what would happen if Homer got a different job, like becoming a famous artist. It would be fun to see how his new career would change the family dynamics.
A time - travel crossover within 'the simpsons crossover fanfiction' is also cool. The Simpsons could travel back in time to the Stone Age or forward to a futuristic world. In the Stone Age, they might have to deal with dinosaurs and primitive living conditions, and in the future, they could encounter advanced technologies that they don't understand.
One idea could be creating an OC who is a new neighbor in Springfield. They could have a really unique hobby, like collecting antique typewriters. This OC could then interact with the Simpson family in various ways, like getting into a friendly competition with Homer over a barbecue recipe.
One interesting idea could be a crossover with "Moana". Elsa's ice powers and Moana's connection to the ocean could create a really cool dynamic. Maybe Elsa accidentally freezes part of Moana's ocean and they have to work together to fix it. Another could be with "Tangled". Rapunzel's long hair and her adventurous spirit combined with Elsa and Anna's journey in Frozen 2 would be exciting. Rapunzel could use her hair to help them climb mountains or cross chasms. A third idea is a crossover with "Beauty and the Beast". Belle's love for books and knowledge could help Elsa understand more about her powers and the history of magic in the Frozen world.
A Thundercats and Star Wars crossover fanfiction would be really cool. The Thundercats could be in the Star Wars universe, and their unique powers and weapons could be a great addition. Maybe the Thundercats could help the Jedi or the Rebels in their fight against the Sith or the Empire. For instance, Cheetara's speed could be useful in battles, and Tygra's illusions could be used to deceive the enemy.
Another could be a fanfiction where Moe has a secret talent for art and Marge discovers it. She then encourages him to show his work in the local art exhibition, which causes a stir in the town as no one expected this side of Moe. This could explore their friendship and how they support each other in achieving new things.
One idea could be a story where Bart and Lisa team up to solve a mystery in Springfield. Maybe there's a strange occurrence at the school and they use their unique skills, Bart's street smarts and Lisa's intelligence, to figure it out.
One idea could be that Slender Man somehow gets transported into the Simpsons' world. He might start lurking around Springfield Elementary, causing the kids, including Bart and Lisa, to feel an unexplained sense of dread. Another plot could involve Homer mistaking Slender Man for a really tall, creepy new neighbor and trying to befriend him in his typical, bumbling way.