One idea could be an OC with the power to manipulate time. They could be a new recruit to the X - Men and struggle with using their power responsibly. For example, they might accidentally send a teammate into a different time period and have to figure out how to bring them back.
A powerful OC with telekinetic and telepathic abilities combined. This OC could be a bit of an outcast even among the X - Men at first because their powers are so strong. They might have to learn to control their emotions to keep their powers in check, and their journey of self - discovery and acceptance within the X - Men team would make for an exciting fanfic.
Maybe an OC who has the power of telepathy but in a very unique way. Instead of just reading minds, they can project their thoughts into the dreams of others. This OC could be used to either help the X - Men by warning them of threats through their dreams or be a villain who uses it to plant false ideas in their heads. They could have a complex backstory about how they developed this power and why they choose to use it in the way they do.
One idea could be creating a male OC who has a unique mutant power related to nature, like being able to control plants. He could join the X - Men and have to learn how to control his powers while also dealing with the prejudice against mutants. Another idea is a male OC who is from a different dimension and has powers that are unknown to the X - Men world. His arrival could stir up a lot of confusion and also bring new knowledge about different types of mutant abilities. And a third idea is a male OC who was experimented on by a shadowy organization before coming to the X - Men for help, and he has to overcome the trauma of his past while learning to use his newly - discovered mutant powers.
One idea could be creating an OC with a unique mutation that has never been seen before in the X - Men universe. For example, the ability to manipulate time on a small scale, like slowing down or speeding up time in a limited area. This OC could be a new student at the Xavier Institute and face challenges in controlling their power while also trying to fit in with the other mutants.
One idea could be an OC who is a new secretary in the office. She has a modern perspective that clashes with the traditional values of the Mad Men era. For example, she might be more outspoken about women's rights and how they are treated in the workplace.
A great 'X Men Crossover Fanfic' idea could involve crossing over with the Buffy the Vampire Slayer universe. The X - Men could help Buffy and her gang fight some really powerful vampires that are immune to normal slayer weapons. Another idea is an X - Men and Doctor Who crossover. The Doctor could land in the X - Men's world and they could team up to stop some time - traveling villain who is trying to change mutant history. There could also be a crossover with the Ghostbusters. The X - Men and the Ghostbusters could work together to stop some mutant - created ghosts that are causing chaos in New York.
A cool 'X Men Ascension' fanfic idea would be to set the story in an alternate universe. Maybe in this universe, the roles are reversed, and the mutants are the ones in power while the humans are the ones feared. How would the X - Men handle this situation? Would they be more benevolent rulers or would power corrupt them? It could be a really interesting exploration of the 'X Men Ascension' concept.
The OC could be a mutant from a different country who comes to the X - Men school. Pietro is immediately intrigued by her different culture and way of using her powers. They start to exchange stories about their mutant experiences, and a relationship forms based on mutual understanding and respect for their differences.
Perhaps a fanfic where Wolverine forms an alliance with some of his old enemies in order to fight a greater threat that endangers all mutants. This would be a story full of tension as they have to trust each other despite their past differences.
Maybe there's a crossover where a mutant has the power to control technology, and this causes a rift between the Transformers and the X - Men at first. But then they realize they need to work together to stop a greater threat, like an alien invasion that's targeting both Earth and Cybertron. The X - Men could use their powers to help the Transformers repair and upgrade in ways they never thought possible, while the Transformers provide the X - Men with powerful new weapons and defenses.
One idea could be Deadpool trying to join the X - Men but constantly causing chaos with his unorthodox methods. He might start off by 'auditioning' in the most over - the - top way, like showing up with a bunch of his chimichanga - loving friends. Another could be Deadpool getting involved in an X - Men mission where his fourth - wall - breaking abilities actually help them in unexpected ways, like when they're facing a mind - reading villain and he can just tell the reader what the villain is thinking.