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.
A possible plot twist could be that one of the Avengers, say Hulk, is actually a long - lost Gem. His transformation into the Hulk could be related to some dormant Gem power within him. This would completely change the way the other Avengers and the Crystal Gems view him.
He could end up altering the entire history of the Gem war. Steven might try to find a way to end the war peacefully much earlier. He could convince the Diamonds to change their ways before things got as bad as they did in the original timeline. This would mean that many Gems who were corrupted in the original story might not be corrupted at all. And the Earth would probably be a very different place, with a more harmonious relationship between the Gems and humans.
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.
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.
One interesting plot twist could be that Steven discovers that he is the one who unknowingly created the time loop in the first place. Maybe his overuse of his powers in a particular situation disrupted the time - space continuum, leading to the loop.
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.
Perhaps the biggest plot twist would be if Future Gohan's time - traveling somehow connects to a greater cosmic force or an ancient prophecy. His journey back in time could be part of a larger plan that he wasn't aware of. This could introduce new enemies or allies that are related to this cosmic plan. It might also mean that his actions in the past are not just about saving his own future, but about saving the entire universe from a much greater threat that was yet to be revealed.
Often, Dean will go back in time and accidentally change something small that has huge ripple effects on the future. Like he might save someone who was supposed to die, and then that person ends up causing a lot of chaos in the future that Dean has to fix. This creates a cycle of trying to set things right again. Another plot twist could be that when he goes back, he meets an alternate version of himself or his loved ones that are very different from what he knows, and he has to figure out how to deal with them.
One common plot twist could be that Naruko discovers she has the power to change not only her own fate but also the fate of the entire village. For example, she might prevent a major disaster that originally happened in the past. Another could be that she finds out a hidden truth about her family or a powerful jutsu that was lost in time. Maybe she realizes that a person she thought was an enemy in the present was actually a friend in the past and has to figure out how to reconcile that in the future.
One popular plot twist could be Killua going back in time and accidentally changing something that has a huge impact on his relationships. For example, he might prevent himself from meeting Gon in the first place, and then has to figure out how to get their friendship back on track. Another could be that he goes back to a time when a great evil was just starting, and he has to stop it before it gets out of hand, which completely changes the future he knew.