A possible crossover could be in the form of music. The ponies could learn MJ's songs and perform them in their own unique pony voices. For example, Twilight Sparkle could sing 'Billie Jean' with her magical voice adding a new twist to the song.
One more crossover could be the concept of unity through music. Michael Jackson was known for bringing people together with his music. In an MLP and MJ fanfic, the ponies could use MJ's music to bring different pony tribes together. For instance, the earth ponies, pegasi, and unicorns could put aside their differences and come together to celebrate MJ's music at a big festival in Equestria. This would show how his music can have a positive impact even in the world of My Little Pony.
Another theme could be the power of music. Michael Jackson's music had a huge impact. In an MLP and MJ fanfiction, it could be about how the power of his music reaches the MLP world and affects the ponies. Maybe it heals the sick or unites different pony tribes, similar to how his music brought people together in our world.
He could be incorporated as a visiting star from another dimension. His presence causes a stir among the ponies, who are both fascinated and inspired by his music and moves. The ponies might learn new ways to express themselves from him.
One interesting Michael Jackson MLP fanfic could be one where he is a magical being in the MLP world. He might use his iconic dance moves to create some kind of unique magic. For example, his moonwalk could be turned into a spell that freezes time for a short moment in the MLP universe.
One interesting fanfic could be about a My Little Pony character who is a huge Michael Jackson fan. In this story, the pony tries to incorporate MJ's dance moves into their own performances in Ponyville. They might hold a special concert where they do the moonwalk and other iconic MJ dance steps, much to the amazement of the other ponies.
A great crossover could involve a battle between the magic of MLP and the power of Pokemon. Imagine Twilight Sparkle using her magic against a powerful Pokemon like Charizard. Or perhaps the Mane 6 team up with a group of Pokemon trainers to fight a common enemy. They could combine their strengths, like Rarity using her fashion skills to create cool outfits for the Pokemon trainers while they battle. It would be a really unique and exciting story.
One idea could be a crossover between MLP and a popular fantasy series like Lord of the Rings. Ponies could take on the roles of hobbits, elves or dwarves in an adventure to save Equestria from a Sauron - like villain. Another could be a crossover with a superhero universe, where ponies gain superpowers and fight against evil forces. Maybe a crossover with a classic fairy - tale world, like Wonderland from Alice in Wonderland, and ponies have to navigate through the wacky and strange world.
In some fanfics, the Hulk might befriend Fluttershy. It's an unexpected pairing but it works. Fluttershy's gentle nature could potentially calm the Hulk down when he's angry. And the Avengers would be introduced to the magic of Equestria, like the Elements of Harmony which could be a key factor in defeating a common enemy.
One interesting crossover could be the use of their powers together. Michael Vey has his electric powers and Percy Jackson has his control over water. Maybe they could combine forces to fight a common enemy like a powerful fire - based monster. It would be a cool display of their unique abilities working in tandem.
A possible plot could be that the child reader is going through a tough time at school and at home, feeling depressed. Michael Jackson, in the fic, could cross paths with the child, like at a concert or in a park. He then notices the child's sadness and starts to befriend the child, using his music and kind words to slowly lift the child's spirits.
A crossover might involve the characters from MLP getting trapped in the Tokyo Ghoul universe. The ponies would have to adapt to this new and dangerous world. Fluttershy, with her gentle nature, might initially be terrified of the ghouls but then try to befriend them through her kindness. Rainbow Dash could use her speed to outrun the ghouls and help the other ponies escape from dangerous situations. It would be a really unique take on both universes.