In this fanfiction, a great plot twist could be related to the origin of Harry's powers. If Tom is his father, it could be revealed that Harry's power is not just from his mother's sacrifice but also from some unique magic that Tom passed on. This could lead to a situation where Harry has to learn to control this new aspect of his magic that he never knew about before. It might also cause conflict within the wizarding community as they question whether Harry is truly on their side, given his newfound connection to Tom.
A great plot twist could be related to their friends. Since they are twins, their friends from Gryffindor and Slytherin are forced to interact more. Hermione and Ron might initially be very skeptical of Draco being Harry's twin. But as they get to know him better through the connection with Harry, they find that there are good sides to Draco that they had never noticed before.
One possible plot twist could be the merging of Warframe's unique movement abilities, like bullet jumping, with Destiny's more traditional FPS movement. Imagine a Warframe character suddenly appearing in the Destiny universe and using their acrobatic skills to outmaneuver the enemies. Another could be the combination of Warframe's Orokin technology with Destiny's alien races. For example, the Vex could start using Orokin energy sources, leading to a whole new level of threat.
A really cool plot twist could be that they find out that they are part of some ancient prophecy. Maybe their union is supposed to bring peace to the land or something. This would force them to deal with a whole new level of responsibility. Or there could be a plot twist where Elizabeth's family loses all their money and Darcy has to figure out how to support them without making Elizabeth feel like she's a burden. Also, it could be that there's a misunderstanding where Darcy is thought to be unfaithful due to some misinformation spread by a jealous rival.
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.
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.
Another great plot twist could be a change in the nature of a well - known hero. In the fanfiction, perhaps Superman loses his powers due to some strange phenomenon in the crossover, and the other members of the Justice League have to step up and protect him while also trying to find a way to restore his powers.
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.
Well, it could be that Harry's glasses start to show him visions of the future or the past. This would completely change his understanding of the wizarding world and his place in it. The glasses might be enchanted by an ancient wizard who foresaw Harry's importance. These visions could lead him on a new quest to either prevent a disaster or uncover a great truth about the origins of magic.
One interesting plot twist could be that Fem Harry's presence among Voldemort's ranks causes internal conflict. Some Death Eaters might be distrustful of her because she was once the 'Boy Who Lived' in a female form. Another twist could be that Fem Harry starts to influence Voldemort's ideology in a way he didn't expect. Maybe she makes him question his pure - blood supremacy by showing that her Muggle - born friends were as powerful as any pure - blood wizard. Also, it could be that her joining was part of a long - con plan to bring down Voldemort from the inside, and she gradually starts to turn his own followers against him.
One possible plot twist could be that Harry discovers he has a long - lost sibling. This would completely change his understanding of his family and his place in the wizarding world. It would also have a huge impact on the relationships he has with other characters, like Dumbledore who might have been hiding this truth from him.