Well, in this 'Harry Potter goes back in time' evil fanfiction, Harry might go back and change things to benefit Voldemort. Maybe he'd stop Dumbledore from finding out important information or interfere with the Order of the Phoenix's formation. He could also use time - travel to learn dark magic from the past and bring it to the present, causing destruction and fear among the wizarding community.
In a 'Harry Potter goes back in time' evil fanfiction, there are numerous possibilities. Harry could become a tool of the Death Eaters if he goes back far enough. He might prevent his own parents from getting together, which would have a huge impact on the future. Also, he could manipulate events so that key good characters like Sirius Black or Remus Lupin are killed early on. This would leave the wizarding world more vulnerable to the forces of evil as there would be fewer people to oppose them.
If Harry Potter goes back in time to teach fanfiction, it would be a really strange and interesting scenario. First of all, the wizarding world might not understand what fanfiction is at first. Harry would have to explain that it's a form of writing where fans create their own stories based on the original. He could inspire young witches and wizards to be more creative with the Harry Potter story itself. Maybe some of them would come up with really unique magical adventures that even J.K. Rowling hadn't thought of. Also, it could cause some chaos as the concept of fan - created stories might be a bit too modern for the old - time wizarding community.
Another possibility is that an evil wizard from the past, who was previously defeated, gets resurrected or empowered by Harry's time - traveling interference. This wizard could then become the main antagonist, using Harry's actions to their advantage and wreaking havoc on the wizarding world.
In fanfiction, if Harry goes back in time to the god, he might gain some extraordinary powers. Maybe the god would bestow upon him the ability to control magic in ways he never could before. It could also lead to him changing the course of history, for better or worse.
Well, they could meet younger versions of themselves and their friends. It would be really interesting to see how they interact. They might also try to give some hints or advice to their younger selves, but they have to be careful not to disrupt the timeline too much. And they could discover secrets that were long forgotten in the present time.
Well, he might try to change certain events. For example, he could prevent Cedric from entering the Triwizard Tournament, thus avoiding his tragic death. He might also use his knowledge of future events to outwit Voldemort earlier.
Definitely Hermione. Since she's Harry's closest friend and very intelligent, she would be deeply involved in any changes Harry tries to make. Also, Snape. Harry's actions in the past could completely change his relationship with Snape. And of course, Voldemort. If Harry goes back far enough, he could potentially stop Voldemort's transformation into the evil wizard he became.
Well, in some 'Harry Potter goes back in time' fanfics, Harry might go back to his first year at Hogwarts. He could then use his more advanced magical skills (from his future experiences) to solve the mystery of the Philosopher's Stone in a completely different way. This might involve him befriending different people earlier or even changing the course of how the challenges in the dungeon were set up.
Well, he might use his magic in ways that Camelot has never seen. Maybe he'd help King Arthur with some tough battles using spells like Expelliarmus. He could also introduce the wizards' world to the knights, which would be really interesting.
Well, he might be really confused at first. Storybrooke has its own set of magic and rules that are very different from the wizarding world. He could start exploring and find some similarities between the magic there and his own. Maybe he'd team up with some of the characters in Storybrooke to solve problems or fight against a common enemy.
In such a fanfiction, Harry might go to Voldemort to try and reason with him. Maybe he believes there's a chance to end the war without more bloodshed. He could offer Voldemort a way out, like exile instead of death.