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.
One possible plot twist could be that when Harry goes back, he discovers that Snape's situation is far more complex than he initially thought. Maybe Snape was involved in some secret mission that put him in danger, and Harry's interference actually endangers the entire wizarding world in unexpected ways. For example, Snape might be on the verge of uncovering a new dark magic plot that Harry's presence disrupts.
One possible plot twist could be that Snape, in his attempt to save Harry, accidentally changes the entire future of the wizarding world. For example, he might prevent Voldemort from ever rising to power in the first place, which would mean that all the relationships and events that we know from the original story would be completely different. Another plot twist could be that Snape discovers that saving Harry is not as straightforward as he thought. Maybe there are dark forces at work that are trying to stop him from changing the past, and he has to fight against them while also trying to protect Harry.
It could be a dark wizard that was previously unknown. Maybe this wizard has a grudge against Harry's family for some long - forgotten reason and is using a very subtle and complex plan to harm Harry. And Fred discovers this wizard's plot when he goes back in time.
One possible plot twist could be that when Lily goes back, she discovers that saving Sev is far more complicated than she thought. Maybe there are forces in the past that are determined to keep the original timeline intact. Another twist could be that in her attempt to save Sev, she accidentally changes something else in the wizarding world for the worse.
One possible plot twist could be that when Luffy goes back, he discovers that Ace's fate is more intertwined with the World Government's secrets than he thought. Maybe Ace was targeted not just because of his bloodline but because he knew something dangerous. Another twist could be that in the past, Luffy has to team up with unexpected allies, like some of the former enemies of the Straw Hats, to save Ace. And perhaps, his time - traveling disrupts the timeline in a way that creates new threats not only to Ace but to the entire world of One Piece.
She could accidentally change other things in the past. For example, her presence might disrupt some other events that were supposed to happen. Maybe she prevents another character from getting a crucial piece of information, which then has a ripple effect on the future.
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 plot twist could be that they end up in the wrong time period completely. Instead of the time they intended to go to, they land in a much earlier era of magic. There, they discover secrets about magic that have been long forgotten in their time. However, they also face the danger of getting stuck there because the magic that sent them back was calibrated for a different time, and they have to find a way to adapt it to return home.
One popular fanfiction with this plot is 'Time's Redemption'. In it, Hermione uses a powerful time - turning device to go back. She faces many challenges in the past, like avoiding detection by other characters while trying to figure out how to prevent Fred's death. It's a great read for those who love emotional and action - packed stories.
One possible plot twist could be that Katniss goes back in time and prevents the Hunger Games from ever starting. Maybe she meets the people who first came up with the idea and manages to change their minds. Another could be that she goes back to a time before her father died and is able to save him, which would completely change her family's situation and her own personality development. A third plot twist might be that she goes back to a crucial moment in the Games and alters the outcome in a way that surprises everyone.