Well, in a crossover fanfiction, the X - Men could be transported to the world of Frozen. Kitty Pryde could phase through Elsa's ice walls, which would be really cool. Magneto could also play a role. If he somehow ended up in Arendelle, he might try to take over the place using his magnetic powers. But the people of Arendelle, along with the X - Men, would have to stop him. It would be a story full of action and adventure, with the unique powers of the X - Men mixing with the charm of Frozen.
One interesting crossover could be the X - Men characters in the world of Westeros. For example, Magneto could use his powers to manipulate the iron in the weapons and armors of the various factions in Game of Thrones. He might side with a particular house, perhaps seeing an opportunity to gain power or protect mutants in this new and different world. Wolverine's healing factor and combat skills would make him a formidable fighter in the battles of Westeros. He could find himself involved in the power struggles, similar to how he gets involved in various conflicts in the X - Men universe.
In some fanfictions, there could be a crossover where Spider - Man gets caught in a time - travel experiment by the X - Men. He ends up in a past era with the early X - Men. There, he has to use his modern - day knowledge and skills to help them against a powerful foe. It could also be a crossover where the X - Men visit Spider - Man's world in Queens and learn about his normal life as Peter Parker, while also helping him fight local villains.
One interesting crossover could be the idea of Hogwarts students having mutant abilities. For example, a student who can control the weather like Storm from X - Men. It would create a whole new dynamic within the Hogwarts environment, with new challenges and friendships.
Well, in some fanfiction, we might see Anna and Kristoff visiting Hogwarts. They could be amazed by the moving staircases and magical creatures. In reverse, Harry, Ron and Hermione could end up in Arendelle. Hermione might be intrigued by the way Elsa controls her ice powers and try to find a scientific or magical explanation for it. Also, the Dementors from Harry Potter could be compared to the dark forces in Frozen 2, like the mist that Elsa has to face.
One interesting crossover could be a scenario where Hermione uses her magic to help Elsa control her powers better. Maybe she creates a spell that can soothe Elsa when she's about to lose control.
One interesting crossover could be Elsa using her ice powers in the Hunger Games arena. She could create ice barriers for protection or freeze her opponents' weapons. Another could be Anna's fearless nature helping her navigate the deadly Hunger Games, forming alliances with other tributes. Maybe characters from Frozen could interact with the Capitol, like Elsa impressing them with her powers during an interview.
In a Percy Jackson - Frozen fanfiction, perhaps Annabeth could meet Anna. Annabeth would be impressed by Anna's determination and loyalty. They could go on an adventure in the Arendelle kingdom, with Annabeth using her strategic mind to solve problems that the Frozen world is facing, like a strange curse that is making the ice in the kingdom melt uncontrollably.
One interesting crossover could be Naruto learning some of the X - Men's powers. For example, he might gain the ability to control magnetism like Magneto and use it in combination with his own chakra control for unique attacks.
If the X - Men were in the Frozen universe, they would bring a new dynamic. Wolverine's healing factor would make him a valuable asset in the cold and dangerous environment. He could withstand extreme cold and any injuries that might come from the ice. Storm could collaborate with Elsa to create more elaborate weather patterns. The X - Men's mutant status could also cause some interesting reactions among the people of Arendelle, who are not used to such extraordinary abilities. It could lead to a story about acceptance and cooperation between two very different groups.
One interesting crossover could be Goku meeting Elsa. Goku might be intrigued by Elsa's ice powers and try to spar with her. He could learn a lot about controlling power from Elsa as she has to constantly keep her emotions in check to avoid causing too much ice mayhem, much like how Goku has to control his Saiyan rage.