There could also be a chance for Harry to improve his relationship with Snape. Knowing how Snape's story unfolds in the future, Harry could try to be more understanding towards him. This could lead to a different dynamic in their classes and interactions, and might even result in Snape being less harsh on Harry throughout the third year.
He might face the challenges of the Marauder's Map all over again. Since he already knows about it, he could use it in new and unexpected ways to outwit his enemies or just to have some fun exploring Hogwarts secrets.
She might encounter strange creatures. In the opposite world, there could be magical beings that are completely different from what she has known in her own world. For example, there could be talking animals with special powers.
He might encounter advanced technology that he has no idea how to use. For example, flying cars or holographic communication devices. It would be really funny to see him struggle with these new things at first.
Ash could meet new friends. The city is filled with different kinds of people. Maybe he'll meet a trainer with a completely different approach to Pokémon battles, which could inspire him to improve his own skills. He might also meet locals who can show him around and introduce him to the hidden gems of Altomare.
In this kind of fanfiction, Percy Jackson would bring his unique demigod skills to the army. Maybe he'd use his water - controlling abilities to help in situations like creating water barriers or putting out unexpected fires. His combat skills, honed from fighting monsters, would make him a formidable soldier. He could also use his ability to sense danger to warn his comrades of impending threats.
She could have an adventure related to the Nile River, which is full of mystery and magic in the wizarding world. There might be magical guardians protecting certain parts of it. Also, in Egyptian fanfiction, the architecture is often a big part of the story. She could be exploring ancient temples and palaces that are full of hidden passages and magical artifacts. Her femininity might also play a role, perhaps she'll be treated differently by the Egyptian magical society as a female wizard compared to how she was treated in the male - dominated British wizarding world.
Well, he could encounter new allies and enemies in different villages and face all kinds of challenges on his own journey.
He might encounter rare Pokémon that are unique to the Johto region, like Chikorita or Cyndaquil as his starter. He could also face off against the infamous Team Rocket, who always seem to be up to no good in the Pokémon world.
His friends, like Ron and Hermione, would be quite surprised. Ron might be a bit jealous at first that Harry has this unique experience of traveling back in time. But then they would realize the potential of it. Hermione would be eager to make sure Harry doesn't change things too much that could have a negative impact on the future.
He might encounter unique and dangerous beasts in Uzushiogakure. Fanfiction often has new and exciting creatures for the protagonist to face, and Uzushiogakure's different environment could be home to such beasts.
Well, in this fanfiction, she could get involved in the American wizarding politics. Maybe there are some power struggles she has to navigate. Also, she might visit famous American wizarding locations like Ilvermorny. There, she could learn about the history of magic in America and how it differs from that in Britain. And of course, she could face some new dark magic threats specific to America.