In certain fanfictions, a really interesting plot twist is when Harry Potter is sent back in time and ends up influencing Tom Riddle's early life in ways he didn't anticipate. This can lead to a completely different Hogwarts and wizarding world. For example, Harry might accidentally introduce a new form of magic that Tom then misuses. Or, there could be a plot twist where Tom Riddle's Horcruxes have an entirely different origin or purpose than in the original books, which throws Harry's understanding of how to defeat him into chaos.
Tom Riddle in fanfic can also be a central character in alternate universes. He might be redeemed in some stories, which is a really interesting take. This could involve him having different experiences that lead him to question his dark desires and ultimately turn away from the path of evil. It gives a whole new perspective on his character.
One plot twist could be that the time travel is not accidental. In a fanfic I read, Dumbledore sent Harry back in time on purpose to try and redeem Tom Riddle. This changes the whole perspective of the story as it shows Dumbledore's more proactive and perhaps riskier side in dealing with the threat of Voldemort.
A really interesting plot twist would be if Harry Potter was somehow transported to Gotham as a child and raised there. He would grow up with a different set of values and skills, and when he discovers his magical abilities later on, he has to balance his newfound magic with the street - smart tactics he learned in Gotham. This would completely change his character and how he approaches the fight against Voldemort. And when Batman eventually meets him, he's not the typical Harry Potter we know from the books. It could lead to a whole new dynamic between them.
One interesting plot twist could be that Harry goes back in time and accidentally changes the sorting of the houses. This would lead to different friendships and rivalries. For example, if he made it so that Draco was sorted into Gryffindor, it would completely change their dynamic. Another could be that he changes the outcome of a Quidditch match in the past, which then has a ripple effect on the school's morale and subsequent events. Maybe Gryffindor loses a crucial match they were supposed to win, and it makes them more determined in other aspects.
One possible plot twist could be that Tom Riddle kidnaps Harry not for the typical reasons like revenge or to gain power over the wizarding world. Maybe he discovers that Harry has some hidden knowledge about a long - lost magic that he wants for himself. Another twist could be that while kidnapped, Harry manages to find a way to get into Tom Riddle's mind and discovers his deepest fears, which he then uses to his advantage to try and escape. It could also be that there are other dark forces at play that Tom Riddle is actually trying to protect Harry from, in his own twisted way, by taking him away from the wizarding world for a while.
One interesting plot twist could be that Hermione's teachings accidentally lead Tom Riddle to an even darker path. Maybe she teaches him advanced magic that he then uses in unexpected and malevolent ways. For example, he could use time - turning magic she showed him to manipulate historical events to his advantage.
One interesting plot twist could be when a potion that was meant to be a simple healing draught accidentally turns into a truth - revealing potion. This might lead to characters revealing secrets they never intended to. Another could be a potion that causes temporary magical ability swaps among the characters, like Blaise and another student, which would create a lot of chaos and new interactions.
A possible plot could be that Tom Riddle is forced to save Harry Potter as part of a magical pact or curse. He initially resents it but as he spends time with Harry, he starts to see the world through Harry's eyes. For example, Harry's kindness towards others, even those who are different or outcasts, could make Riddle question his own beliefs. The fanfic could then focus on how Riddle tries to balance his old dark desires with his new - found respect for Harry and the values Harry represents. There could be a lot of internal conflict within Riddle as he tries to decide whether to fully embrace this new path or return to his old ways.
One great plot point would be if the soulmate connection allows them to share each other's memories. Harry would see Tom's difficult childhood, which might make him more empathetic towards him. Tom, on the other hand, would see Harry's experiences of love and friendship. This could lead to a major change in Tom's character. Also, the plot could involve them trying to hide their relationship from Dumbledore, who might see it as a dangerous experiment that could disrupt the balance of the wizarding world.
A fanfic might explore how Harry Potter and Tom Riddle discover they are soulmates. It could start with strange dreams or premonitions that Harry has about Tom. As they get closer, they realize that their destinies are intertwined. This could lead to a conflict within the wizarding world as many would be against their union, seeing Tom as the future Voldemort, but Harry believes in the power of their soulmate bond to change Tom for the better.