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.
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.
A great plot twist could be related to the time - travel itself. What if the way time - travel works in the WW2 era is different from how it is in Harry's time? This could lead to him getting stuck or being unable to use his magic properly. Or perhaps he discovers that a certain event in WW2 was actually caused by a wizard from the future (not just him) who was trying to correct something in the wizarding world's past. His attempts to fix things could then make the situation even more complicated as he unknowingly steps on the toes of a much larger time - traveling plan.
Well, perhaps a plot twist could be that when Kirito goes back in time, he discovers that his own existence in the past was a key factor in creating the problems he faced in the future. So, he has to figure out a way to change things without erasing himself. Or, he could go back and find that the person he loves in his original timeline has a completely different personality or role in the past, which throws him off and makes his feelings really complicated.
A simple plot could be that there is a lemon - themed magical competition at Hogwarts. Harry teams up with Fred and George to participate. They have to create the best lemon - based potion or spell. They struggle at first as they can't find the right ingredients related to lemons, but then they discover a secret stash of rare lemon - scented herbs in the Room of Requirement which gives them an edge in the competition.
A possible plot twist is that when Harry goes back, he realizes that the Marauders are not exactly as he imagined them. There could be secrets within the group that he uncovers. For instance, James Potter might have had a different side to him that was not shown in Harry's original understanding. This discovery could make Harry question his own identity and his relationship with his father. Also, the time - travel could be a trap set by a dark force. Harry might find himself in a situation where he has to fight against this dark plot while trying to maintain the integrity of the timeline.
A plot twist might be that when Luke goes back in time, he finds out that the Force has a different set of rules in the past. This could lead to him having to relearn how to use the Force in this new 'historical' context. He could also meet characters that were thought to be long dead in his time, and these characters could either be allies or enemies. For instance, he might encounter an ancient Sith Lord who was thought to be only a legend. This would create a whole new set of challenges for Luke as he tries to find his way back to his own time while dealing with this unexpected threat.
One possible plot twist could be that when they go back in time, they accidentally change a small event that has huge consequences in the present. For example, they might prevent a meeting between two people that was crucial for the formation of a powerful coven, and now they have to figure out how to fix it before they return to their own time.
One possible plot twist could be that Dark Naruto tries to change the past to prevent his own dark transformation. He might attempt to save someone important who in the original timeline led him down the dark path. For example, if it was the death of a certain character that made him turn dark, he could go back and try to save that person. This would completely change the future and the Naruto we know from the original story.
A possible plot twist is that Kakashi goes back in time and finds out that the events he thought were true in the past were actually misinformation. This could completely change his perception of the history of the ninja world and his own role in it. Also, he might go back to a time when Orochimaru was just starting his dark experiments. Kakashi could try to stop Orochimaru right from the start, but in doing so, he might end up creating new villains or problems. Or perhaps, when he travels back, he loses some of his memories from the future, which makes it difficult for him to use his knowledge effectively to change things.
It could be part of a magical experiment gone wrong. Fred and George are working on a new spell that has something to do with making people feel extreme sensations. By accident, when they test it on Harry, it turns into a tickling sensation. So they have to figure out how to reverse the spell while Harry is being tickled non - stop and is both laughing and begging them to stop.