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.
Captain America's noble and leadership - driven personality would likely mesh well with Princess Celestia's regal and wise nature. They could both inspire their respective teams, the Avengers and the ponies. Meanwhile, Thor's god - like and somewhat brash personality might be an interesting contrast to Pinkie Pie's hyper - energetic and random nature. It could lead to some really funny and also touching moments in the fanfic as they get to know each other.
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 avengers and flash fanfic, there could be a team - up against a common enemy. For example, a villain who can manipulate time. The Flash with his speed and the Avengers with their diverse powers would have to work together. The Flash could be the first to engage, using his speed to scout and gather information. Then the Avengers could come in with their strategic plans. Hulk might be a bit confused by the Flash's quick movements at first but would soon realize he's on their side.
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.
Well, in a crossover, the ponies could have a ship of their own, like a flying ship made of clouds or something really magical. They could cross paths with the pirates during a storm. The ponies' ship could be immune to some of the bad weather effects because of their magic. And then they team up with the pirates to find a hidden treasure that requires both the pirates' seafaring skills and the ponies' magic.
Maybe the Avengers are shrunk down to the size of ponies and end up in Equestria. They have to adapt to the new world and its rules. Iron Man could try to build new tech using Equestrian resources, and Captain America could use his leadership skills to form an alliance with the ponies against a common threat, like a dark magic - based enemy that wants to take over both worlds.
One interesting crossover could be the use of magic in the Avengers' world. For example, Harry Potter characters could teach the Avengers some basic spells to help them in their battles. Another aspect could be the characters' personalities interacting. Hermione might befriend Bruce Banner and they could exchange knowledge about science and magic.
A crossover might involve character pair - ups. Maybe Hawkeye could team up with Deadshot. They are both expert marksmen, and it would be cool to see how they compare their skills and different moral compasses while on a mission together. Another possibility is Black Widow and Harley Quinn. Their contrasting personalities, one being a highly - trained spy and the other a deranged but brilliant criminal, could lead to some really interesting interactions.
One interesting crossover could be the Avengers having to deal with the dinosaurs in Jurassic World. Maybe Iron Man uses his technology to try and control the dinosaurs or Thor uses his powers to fight off the really big ones like the T - Rex. It would be a really chaotic but exciting scenario.