In a 'Mario Meets Peach Fanfiction', a possible plot twist could be that the Mushroom Kingdom is not what it seems. It turns out that there is a parallel dimension where everything is reversed. Bowser is actually the good guy trying to protect Peach from an evil Mario. When Mario enters this parallel dimension, he has to face his own evil self. Another plot twist could be that Peach has a secret power that she has been hiding all this time. When Mario is about to be defeated by Bowser, Peach uses this power to not only save Mario but also to defeat Bowser once and for all. And a third plot twist could be that there is a third party involved, a new character who wants to take over the Mushroom Kingdom and has kidnapped Peach as part of their plan. Mario has to team up with Bowser to defeat this new threat.
Well, a really interesting plot twist in 'Mario Meets Peach Fanfiction' could be that Mario himself is the one being tricked. Bowser has created a fake Peach to lure Mario into a trap. And while Mario is busy trying to rescue the fake Peach, the real Peach is actually in another location, in even greater danger. Also, there could be a plot twist where the power - ups that Mario usually relies on are actually cursed this time. When he uses them, they cause more harm than good. Maybe the super mushroom makes him too big to fit through the narrow passages he needs to reach Peach. Another possibility is that Peach has fallen in love with someone else in the time she has been captive, and Mario has to deal with this new emotional situation.
A possible plot twist could be that Videl turns out to have some hidden powers herself. It would completely change the dynamic between her and Gohan.
A plot twist might be that Jotaro loses his Stand abilities temporarily and McCree has to protect him. Or perhaps they find out that there's a traitor among the people they thought were their allies in this fanfiction world. This would force them to re - evaluate their situation and who they can trust. Also, it could be that a powerful artifact they were supposed to protect actually has the power to control them, and they have to fight against its influence.
One possible plot twist could be that Cersei pretends to surrender to Daenerys. Daenerys, believing her, takes Cersei into her confidence. But Cersei is actually plotting a big betrayal from within. She could be secretly gathering her remaining forces and planning to assassinate Daenerys when the time is right.
In the 'naruto meets nagato fanfiction', a plot twist might be that Nagato fakes his change of heart at first. He could be playing a long - game to deceive Naruto and the Leaf Village. Or perhaps, there is a prophecy that involves both of them, but it has been misinterpreted all along. And when they meet, they start to uncover the real meaning of the prophecy, which changes everything they thought they knew about their fates and the future of the ninja world.
One possible plot twist could be that Bowsette turns out to have some sort of connection to Naruto's world that he never expected. Maybe she has a hidden kekkei genkai - like ability that is related to Naruto's ninja powers.
A possible plot twist could be that the dragon is actually a shapeshifter and turns into a human form that Shirou knows. Maybe it's someone he thought was dead.
One possible plot twist could be that the Dursleys are actually under a spell that makes them act so horribly, and Hermione discovers and breaks it. Another could be that Hermione finds out she has some family connection to the Dursleys, which would be a huge shock for everyone.
Well, in a 'Mario Meets Peach Fanfiction', it might start with Peach sending out a secret signal that only Mario can detect. Mario, being the heroic plumber he is, immediately sets off. He encounters some really strange enemies this time, not the usual Goombas or Koopas. These new enemies are made of ice and fire, alternating their attacks. But Mario uses his quick thinking and his trusty jumps to get past them. When he gets to Peach, she has a special gift for him - a star - shaped medallion that gives him extra strength for future adventures.
A plot twist might be that Videl is actually related to one of Gohan's enemies in some way. This would create a huge conflict between them. Also, it could be that there is a prophecy about Gohan and Videl that they are not aware of, and when they find out, it completely changes their relationship. Maybe Gohan loses his powers temporarily, and Videl has to protect him, which is a role reversal from what is expected in the DBZ world.
A possible plot twist could be that Vegeta Jr is actually an imposter sent to deceive Vegeta. He could initially seem like a legitimate Saiyan but gradually reveal his true motives, which might be related to an enemy's plan to take down Vegeta.