If Harry goes back in time to fourth year in fanfiction, he'll face several challenges. Firstly, he has to be careful not to arouse suspicion among the teachers and students. His knowledge of future events might make him act in ways that seem odd. Secondly, he can't be sure that his actions will actually lead to positive outcomes. For example, if he tries to prevent Cedric from being chosen for the Triwizard Tournament, it could lead to someone else getting hurt. Also, he has to deal with the fact that Voldemort's supporters are still around and might notice his strange behavior and try to figure out what he's up to.
One challenge could be not being able to change things as easily as he thinks. Time might have its own rules. Another is that he might accidentally change something that has a much worse consequence later.
One challenge Clark might face is changing the future too much. If he alters significant events, it could have unforeseen consequences. For example, if he saves someone who was supposed to die, that person's actions in the future might cause more harm than good. Another challenge is dealing with his younger self. He has to be careful not to expose his identity or give away too much information. Also, he might face challenges in terms of fitting into the time period. The technology and social norms of the past could be very different from what he's used to in his own 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.
One challenge Naruto might face is getting used to magic. Since he's used to chakra - based powers, the concept and use of magic could be quite confusing at first. Also, the rules and culture of Fairy Tail might be different from what he's used to in Konoha. He'd need to adapt to the guild's way of doing things.
He might have trouble adapting to the past and avoiding changing events that could have unforeseen consequences.
One challenge could be Ron. Since Ron is their friend, and he has his own feelings for Hermione, this could create a lot of tension. Harry might feel guilty about his feelings for Hermione because of Ron. Another challenge could be the expectations of the wizarding community. They are both well - known in the wizarding world, and their relationship might draw a lot of unwanted attention.
They might face the challenge of not being recognized by their past selves or other characters. Also, they could accidentally change things in a way that creates new and more dangerous villains. Another challenge could be dealing with the technology and power levels of the past, which are much lower than what they are used to.
He might face opposition from the wizarding authorities. Resurrecting the dead is generally not allowed in the wizarding world, so he could get into a lot of trouble.
He might face challenges in terms of curriculum development. There would be pressure to update the courses to keep up with the changing times in the wizarding world. Additionally, he would need to handle the security threats that still lurk, such as the remaining Death Eaters or new dark forces. He has to protect the students and the school's secrets while also allowing for a free and open learning environment.
One challenge could be the Time - Turner rules. If they are using a Time - Turner, they need to be very careful not to break any of the laws regarding time travel. For example, they can't be seen by their past selves or make significant changes that would disrupt the future they come from. Another challenge is the danger of the time period they visit. If they go to a time when Voldemort was active, they are at great risk of being detected by Death Eaters.
One challenge would be making friends. The students at Mahoutokoro might have different values and social norms compared to Hogwarts. He might find it difficult to fit in and find a group he belongs to. Additionally, the academic system could be very different. The grading system, the types of courses, and the way knowledge is imparted could all pose difficulties for Harry.