One interesting plot twist could be that Thor goes back in time and accidentally changes something that makes him lose his powers. For example, he might prevent the event that led to him getting Mjolnir, and then has to find a new way to be a hero without his trusty hammer. Another could be that he goes back and meets a younger version of Loki who doesn't yet hate him, and he has to figure out how to keep it that way so that their relationship in the future is different.
Well, perhaps Thor travels back in time and finds out that there was a prophecy about him that was hidden from him in the future. This could lead to a whole new set of adventures as he tries to figure out what it means and how it affects his future self. Or, he could go back and meet an ancestor who was a great hero, but also learn that this ancestor had a dark secret that could have implications for Thor's own heroism.
A possible plot twist is when Thor goes back in time and discovers that his father Odin was actually from a different realm originally. This revelation could change Thor's entire understanding of his family history and his place in the cosmos. Also, he could go back to a time when Asgard was at war with a long - forgotten enemy, and he has to use his knowledge from the future to either prevent the war or win it in a different way than before.
One interesting plot twist could be that when Lucy goes back in time, she discovers that her family has a much darker secret than she ever knew. Maybe they were involved in some sort of magic that was considered forbidden in the past. Another could be that she accidentally changes the future in a way she didn't expect, like making her friends not become the people she knew them as. And perhaps she finds out that an enemy in the present was actually once an ally in the past, and she has to figure out what went wrong to turn them into an enemy.
One interesting plot twist could be that Naruto, with his knowledge of the future, tries to prevent certain tragedies but ends up causing new ones. For example, he might try to save a character too early and disrupt the natural flow of events, leading to unforeseen consequences.
Well, sometimes in these fanfictions, a plot twist might be that Sirius goes back in time and discovers a hidden truth about his family. Maybe he finds out that there was a secret alliance or a hidden enemy within the Black family that was influencing events all along. This could completely change his perception of his family's past and his place in it. Also, he could go back in time and end up being involved in a different kind of magic that was lost in his original time, like an ancient form of magic that has the power to either save or destroy the wizarding world.
One possible plot twist could be that when they go back in time, they accidentally change something that has a huge impact on their future relationships. For example, Naruto might unknowingly prevent Sasuke from leaving the village in the past, which could completely change how they interact in the present they return to. Another could be that they find out a hidden truth about their parents or the village's past that was covered up, like a secret alliance that their predecessors were involved in.
One possible plot twist could be that Oliver goes back in time and accidentally changes something that makes his friends turn into enemies in the present. For example, he might prevent an event that was crucial for the formation of their friendships. Another could be that he meets a younger version of himself and has to convince that version to make different choices without revealing too much about the future. It could also be interesting if he goes back to a time when his city was in a different state, like before the rise of a major villain, and he has to stop that villain from ever emerging in the first place.
One possible plot twist could be that when they go back in time, they accidentally change something that has a huge impact on the present. For example, they might prevent the sorting hat from putting them in their original houses. This could lead to a completely different dynamic at Hogwarts, with different friendships and rivalries forming.
A really interesting plot twist could be that Steven goes back in time and discovers that the Diamonds had different motives than he originally thought. Maybe they were being influenced by some other force in the past, and by going back, he uncovers this mystery. Also, he could find out that some of the things he thought were his friends' ideas were actually planted by an outside source long ago. This would completely change his understanding of the relationships and history in the Steven Universe world.
One possible plot twist could be that Jon Snow goes back in time and accidentally changes something that leads to a completely different future for the Stark family. For example, he might prevent Ned Stark from going to King's Landing, which would change the power dynamics in Westeros entirely.
Perhaps the writer goes back in time thinking they can use their knowledge of the future to their advantage, but instead they find that the past has its own rules and forces that prevent them from doing so. For instance, every time they try to introduce a future concept, it gets distorted or erased by some mysterious force, adding a sense of mystery and frustration to the story.
Well, perhaps when Fred goes back, he discovers that the danger to Harry is much more complex than he initially thought. There could be a traitor among the people he thought were allies in the past. Also, Fred himself might get stuck in the past and has to find a way to get back while still ensuring Harry's safety. Maybe the time - traveling magic is being manipulated by a hidden enemy, and Fred has to figure out who and how to stop it to save Harry.