One common theme is fixing past mistakes. Fans often write about characters going back in time to prevent a tragic event like a character's death or a major battle loss. For example, in many fanfictions, someone might go back to stop Thanos from getting the Infinity Stones.
One great MCU time travel fanfiction is 'Time's Echo in the MCU'. It has an interesting plot where a minor character gets the power to time travel and tries to change some key events in the MCU timeline. Another is 'Back to the Origins: MCU Time Travel'. It takes the readers on a journey with a character who travels back to the very first Avengers event and causes some unexpected twists.
If Spider - Man travels back in time, it could strengthen his relationship with Uncle Ben. He might get a chance to really talk to him and understand his values better, which would in turn make him a better hero in his own time. Also, his relationships with his friends like Ned and MJ could be affected. For example, if he changes something in the past, he might come back to a different present where their relationships have shifted.
One idea could be that Spider - Man travels back in time to the moment when Uncle Ben was killed. He tries to prevent it, but realizes that changing this event would have unforeseen and disastrous consequences for the future. So, he has to watch it happen again, but this time he gains a new perspective on his powers and responsibilities.
Some Flash time travel fanfics play with the idea of time travel via dreams. Barry Allen could enter a dream - like state where he experiences different timelines. It's an interesting take as it blurs the line between reality and the subconscious.
One way to create a Kryptonian OC (Original Character) in MCU fanfiction is to first understand the basic traits of Kryptonians in the DC lore. Kryptonians are known for their super strength, flight, heat vision etc. In an MCU context, you could blend these traits with the existing MCU universe's rules. For example, how would a Kryptonian's powers interact with the Infinity Stones? Maybe your OC could be a Kryptonian who was sent to the MCU universe by some cosmic accident. Their journey could involve learning about this new universe while also trying to hide their true identity as they are far more powerful than most beings there.
One common trope is the 'fish out of water' situation. The time - traveling character is suddenly in a different era and has to deal with the strange customs, technology, or social norms. For example, a modern - day character going back to the Middle Ages and being shocked by the lack of indoor plumbing. Another is the 'butterfly effect' trope. Small changes the time traveler makes in the past can have huge, unforeseen consequences in the future.
First, try to blend in. Don't draw too much attention to yourself. If you're in a city, find a normal job and a place to live. Second, if you encounter any threats, use your knowledge of the MCU to your advantage. For example, if you know where the bad guys are going to strike next, you can warn the heroes or get out of the way. And finally, make some friends. Allies are important in the MCU, whether they're normal people or super - heroes.
Another way time travel works in these fanfictions is through dreams or visions that turn out to be more than just that. A character might have a really vivid dream about the past or future in Riverdale, and then suddenly find themselves actually in that time period. This method allows for a more psychological exploration of the character as they deal with the shock of suddenly being in a different time and having to figure out what's real and what's not.
In some RWBY time travel fanfiction, it might work through the use of a special relic. The relic could have powers that are not fully explored in the original series but in fanfiction are used for time - traveling. For example, it could be activated by a specific combination of Dust or a certain type of Grimm blood.