Perhaps when Bilbo travels back in time, he finds that the Ring has an unexpected origin or connection to other powerful artifacts. This could lead to a whole new set of challenges and adventures as he has to deal with these new revelations while still trying to destroy the Ring. For example, he might find that the Ring is part of a set of items that need to be dealt with together in a specific order.
Bilbo might adapt by using his wits. He's always been a clever hobbit. In an earlier time period, he could use his knowledge of future events to his advantage. For example, if he travels to a time before the discovery of certain paths in Middle - earth, he could be the one to find them first, which would help him in his quest to destroy the Ring.
Well, a really interesting plot twist in an Eren travels back in time fanfiction could be related to relationships. Say Eren goes back and realizes that his actions in the past have a huge impact on his relationships with his friends. Maybe he accidentally causes Mikasa to not be as attached to him as she was in the original timeline. Or he could find out that Armin was supposed to be the one with the time - traveling ability all along, and his interference messes up Armin's future plans. Also, what if he goes back and discovers that the real enemy wasn't the Titans but some other force that was using the Titans as a distraction, and his time - traveling journey is the only way to expose this truth.
A plot twist could be that Sakura travels back in time and realizes that the world she thought she knew was all a lie. The history books in her time were wrong. She could find that the origin of her magical powers was something very different from what she was taught. Also, she might go back to a time when there was a powerful artifact that was lost in her own time. However, when she tries to retrieve it, she discovers that it has a dark side that she didn't expect. This could lead to a moral dilemma for her, whether to keep it or leave it be.
Well, a really interesting plot twist might be that when Merlin travels back in time, he discovers that the future he thought he knew was all wrong. Maybe the events that led to Arthur's rise and fall were actually set in motion by a time - traveling sorcerer from even further in the future. He could also find that the people he thought were his allies in the past were actually working against him all along, which would completely change his view of history and his role in it.
Perhaps Tony travels back to a time before a key technology was developed in his world. He then has to figure out how to recreate that technology with the limited resources of the past. This could lead to some really interesting interactions with the scientists of that era. Also, he might accidentally introduce some future concepts that are far ahead of their time, which could cause a stir among the intellectual community. And if he changes the development of this technology too much, it could have a huge impact on the future he came from.
Well, a really interesting plot twist might be that when Rick travels back in time, he discovers that time is actually a loop. So all his actions in the past were already pre - determined and he was just fulfilling his part in the loop. This could lead to a whole existential crisis for Rick as he realizes he may not have as much control as he thought. Or perhaps he goes back and finds out that an enemy from the future has already been manipulating events in the past to try and stop Rick from ever becoming the genius he is.
One exciting plot twist could be Octavia traveling back in time and accidentally changing a key event that led to the creation of the Ark. This would completely rewrite the history of the 100. Another could be her meeting a younger version of herself and trying to guide her without revealing her true identity. It would create a lot of internal conflict for Octavia as she sees her younger, more naive self.
One possible plot twist could be that in the other dimension, Naruto finds out that all his friends have different personalities. For example, Sasuke could be a peaceful scholar instead of a brooding avenger. Another twist might be that the chakra system works completely differently in this new dimension. Maybe instead of using hand signs, they use some kind of mental power to perform jutsus. Also, Naruto could discover that the Akatsuki in this dimension are actually the good guys, fighting against an evil ninja clan that wants to take over the world.
One common plot twist could be that the end, when traveling back in time, accidentally changes something that has a huge ripple effect on the future. For example, they might prevent an important event from happening that was crucial for the development of a certain technology or the rise of a key character. Another plot twist could be that the end realizes they are not actually in their own past but in an alternate timeline. This can lead to a whole new set of challenges as they try to figure out how to get back to their own timeline or if they should even try to change things in this new one.
One interesting plot twist could be that Minato travels back to a time when the Hidden Leaf Village is on the verge of a civil war. He uses his future knowledge to prevent it, changing the entire future of the village. Another could be that he travels to a time where his parents are still alive and has to deal with the complex emotions of seeing them again.