Another trope is the 'alternate universe' where the X - Men and MCU have a completely different relationship or history. For instance, in some fanfictions, the X - Gene is a result of some Avengers - related experiment. This trope gives a lot of creative freedom to the writers and can lead to some really unique stories.
One common trope is the 'fish out of water' where the X - Men characters are suddenly in the MCU and have to adapt to the different rules and characters. For example, in many fanfictions, Wolverine has to deal with the high - tech world of the Avengers.
The 'team - up against a greater threat' trope is also popular. It often involves the X - Men and the Avengers coming together to fight a powerful villain like Thanos or a new super - powered baddie created just for the fanfiction. This trope allows for some epic battles and interesting character dynamics.
One great 'X Men MCU Fanfiction' is 'The New Mutants in the MCU'. It's an exciting story that imagines how the young mutants would fit into the MCU. It has great character development and action scenes.
Fanfiction.net is another good place. There are many writers who post their MCU x Men fanfictions there. However, the interface might be a bit more difficult to navigate compared to AO3. But with some patience, you can find some really interesting stories that combine the two universes.
One good MCU x Men fanfiction could be 'The Unlikely Alliance'. It's about the Avengers and the X - Men coming together to fight a common enemy from another dimension. The story is exciting as it combines the unique powers of both groups and shows how they overcome their initial differences.
In Grey's Anatomy fanfiction, the 'forbidden love' trope is quite popular. This could be between two doctors who are in different positions in the hospital hierarchy or have some other obstacle to their relationship. In X - Men fanfiction, the 'outsider' trope is common. New mutants coming into the X - Men group and feeling like they don't belong at first. When combined, you might have a story where a Grey's Anatomy character who is an outsider in the hospital (maybe a new intern) discovers they are a mutant and feels like an outsider in both worlds.
There's the 'legacy' trope. The male OC could be related to a famous MCU character and has to live up to their name or break free from their shadow. For instance, he could be the son of a fallen hero. Another trope is the 'chosen one' trope. He's the only one who can defeat a certain big bad in the fanfic. And the 'mentor - mentee' trope, where he either mentors a younger character or is mentored by an established MCU hero like Captain America or Iron Man.
In this type of fanfiction, the 'wise old mentor' trope might be used. An older, more experienced Nalu man could guide the younger ones in the ways of war. The 'treacherous ally' trope is also possible. One of the groups they thought was an ally turns out to be working against them, adding more drama to the story. Additionally, the 'mysterious power - up' trope can occur. A Nalu man discovers a new power or ability during the war that helps turn the tide of battle.
A common trope is the 'fish - out - of - water' situation. The OC, being from a normal world, is completely out of their element when dealing with Slenderman and his spooky realm. Another popular trope is the 'damsel in distress' or 'heroic OC' dichotomy. Sometimes the OC is portrayed as a helpless victim that Slenderman preys upon, while other times they are the brave hero who tries to fight back or outwit him.
A less common but still interesting trope is the 'reincarnation' trope. In some fanfictions, Garroth and Laurence are reborn in different lifetimes and keep finding each other. This trope allows for exploring different historical or fantastical settings while still maintaining the core of their relationship. It gives the authors a chance to be creative with different time periods and how their relationship adapts in each one.
One popular trope is the 'enemies to lovers' trope. Given their different outlooks and Homelander's often villainous actions, this is a common way to build a relationship in fanfiction. Another is the 'power imbalance' trope, where Starlight has to deal with Homelander's overwhelming power.
A less common but still interesting trope is the 'swap of roles' in Thorfinn x Canute fanfiction. For instance, Thorfinn might find himself in a position of political power for a while, while Canute has to rely on his combat skills. This trope can lead to a lot of interesting character exploration and development as they both have to adapt to new situations outside of their comfort zones.