A great plot twist could be that Jacob discovers he is not actually a werewolf but a hybrid of some sort, created by an ancient magic that the Quileute tribe has long forgotten. This would make his relationship with both the vampires and his own pack very different and full of new tensions.
A possible plot twist could be that a maester discovers a way to use steam power to bring the dead back to life in a more controlled way. This would completely upend the power dynamics in Westeros. The Night King would no longer be the sole controller of the undead, and different factions might try to use this new - found 'life - giving' power for their own gains, whether it's to replenish their armies or to use the undead as a workforce in the new industrial settings.
One possible plot twist could be that Dabi forgets his hatred for his family. This would completely change his dynamic with his father, Endeavor. Instead of seeking revenge, he might start to question the reasons behind his former animosity. Maybe he'll even try to reconcile with his family members, which would shock everyone around him, especially those in the League of Villains who were counting on his vendetta to fuel their plans.
One possible plot twist could be that the kidnappers are not who they seem. Maybe they are being controlled by an ancient evil force that wants to use Legolas for some dark ritual. Another twist could be that Legolas is kidnapped as a decoy to draw out his friends, and then the real target is revealed later. For example, the kidnappers might be after a powerful elven artifact that Legolas's friends possess.
A possible plot twist is that Naruto's time travel sends him to a parallel universe instead of his own past. In this universe, all the characters he knows have different personalities or roles. For example, Sasuke could be a happy - go - lucky person instead of brooding and revenge - driven. Naruto would then have to adapt to this new world while also trying to find a way back to his own universe. Or, he could find out that in this parallel world, the Akatsuki are the good guys, and he has to reevaluate his views on good and evil.
One interesting plot twist could be that they discover their twin bond gives them shared magical abilities that are unique. For example, they might be able to combine their powers to create a new kind of spell.
One interesting plot twist could be that Itachi has a hidden motive that is actually to protect Sasuke from a greater threat. Maybe there's a powerful enemy that Itachi knows will target Sasuke, so he kidnaps him to keep him in a secret location and train him in secret. Another twist could be that Itachi is being controlled by some dark jutsu and he doesn't really want to kidnap Sasuke but has no choice. This could lead to a journey of Sasuke trying to break the control over Itachi. Also, it could be that Itachi kidnaps Sasuke to reveal some long - hidden family secrets that Sasuke needs to know in order to become stronger.
One interesting plot twist could be that Percy discovers a hidden power within himself much earlier. Since he already has the experience of his first life, he might be more in tune with his demigod abilities. Another twist could be that he decides to side with different gods in the power struggles, changing the whole political landscape of the demigod world.
Perhaps a plot twist could be that Naruto and Madara's mother was from a powerful and secret clan. This clan has a prophecy about two brothers saving or destroying the shinobi world. Naruto and Madara are unaware of this prophecy until later in the story. As they start to discover their true potential together, they realize that they have a choice to make. This could lead to internal struggles within each of them as they decide whether to fulfill the 'saving' part of the prophecy or be swayed by Madara's past desires for power and destruction. It would add a layer of mystery and moral dilemma to the fanfiction.
A great plot twist could be that Naruto turns out to be a half - vampire. It would completely change his character arc and how others in the Naruto world perceive him.
One interesting plot twist could be that Bella discovers a way to block Edward from reading her mind temporarily. This would create a new level of mystery for Edward and make him realize how much he relied on that ability. Another could be that when Edward reads Bella's mind, he misinterprets some of her thoughts which leads to a big conflict between them, even though Bella didn't actually mean what he thought.