One interesting plot twist might be that the stepmother and stepsisters are working with the Decepticons. They try to stop Cinderella from getting to the ball because they know she has a connection to the Autobots that could turn the tide of the war. And when Cinderella finally does get to the ball, it's not just a regular ball but a gathering of Transformers and humans to form an alliance. And Cinderella is the key to making this alliance work.
A great plot twist could be that one of the main villains in Ladybug is actually an animal from Zootopia who has somehow gained access to a Miraculous. This would completely change the dynamic as the Zootopia characters would have to face one of their own kind gone bad. It would also force Ladybug and Chat Noir to understand the different motives and behaviors of animals.
In a Naruto and Ben 10 crossover fanfiction, an exciting plot twist could be that the DNA of the aliens in Ben's Omnitrix starts to mix with the chakra in Naruto's world. This could result in new forms for both Ben and Naruto. For Naruto, he might gain the ability to transform into a half - alien, half - ninja hybrid with unique powers. Ben, on the other hand, could find that his alien forms now have chakra - based abilities. This would not only change their powers but also how they interact with their respective worlds and enemies.
In a Naruto - Overlord crossover fanfiction, a great plot twist would be if the Ainz Ooal Gown guild members thought that the Sharingan was a powerful and unknown form of magic. They might try to study it or even recruit Sasuke, who has the Sharingan, into their ranks. This would create a complex situation where Sasuke has to decide between his loyalty to Konoha and the allure of the new and powerful world of Overlord.
One interesting plot twist could be the characters swapping their powers. For example, Naruto's shadow clone jutsu being used by a Fairy Tail mage. This would completely change the dynamics of battles in the Fairy Tail world. Another could be a villain from Naruto teaming up with a dark guild in Fairytail, creating a more menacing threat that both universes have to face together. Also, imagine if the nine - tailed fox somehow got involved in the magic - filled world of Fairytail, it would be a huge disruption and lead to some really unexpected story developments.
One interesting plot twist could be that Soldier 76's time - traveling abilities (if we assume some extended lore) bring him to the RWBY universe during a crucial moment in a battle. His military tactics and advanced weaponry completely change the tide of the fight. Another could be that in the crossover, Soldier 76 has some sort of connection to one of the RWBY characters' pasts, like he was involved in an event that shaped their family history. And a third plot twist might be that his healing abilities become a key factor in saving a major RWBY character from a near - fatal injury, leading to a new alliance between him and the RWBY team.
Well, a great plot twist could be if the Hokage's hat in Naruto's world is somehow connected to a powerful relic in the Castlevania world. Naruto has to journey through the spooky Castlevania realm to find out how to protect the hat and its power from evil forces. Also, imagine if Alucard from Castlevania has a doppelganger in the Naruto world who is a powerful ninja. When they meet, they initially fight but then realize they have a common goal against a greater evil that is threatening both their worlds. And perhaps the Curse Seal in Naruto could be related to the dark magic in Castlevania, causing Naruto to struggle with a new kind of internal darkness that is different from what he's used to.
A common and interesting plot twist is when the magic from the Harry Potter world can affect the vampires in Twilight in unexpected ways. For example, a spell might make a vampire temporarily lose their super strength or their ability to compel. This turns the tables on the usual power dynamics in the Twilight universe.
One interesting plot twist could be the discovery that the Philosopher's Stone in the Fullmetal Alchemist world has a connection to the chakra system in Naruto. Maybe it could be used to enhance or disrupt chakra flow in a way that no one expected. Another could be a character from Naruto, like Naruto himself, accidentally using alchemy due to some strange cross - world magic. This would completely change the dynamic as he tries to figure out this new power while still having his ninja abilities.
One possible plot twist is that the hogyoku from Bleach somehow ends up in the hands of a character in Highschool DxD. This could lead to a character attempting to use it for their own gain, perhaps to gain ultimate power over both the devils and the angels. Another interesting plot twist is that a character from Highschool DxD gets reincarnated as a Soul Reaper in Bleach. They would have to learn the ways of the Soul Reapers while still retaining some of their previous abilities and memories. This could create some really interesting character development. A third plot twist could be that the balance between the three factions in Highschool DxD (devils, angels, and fallen angels) is disrupted by the arrival of Hollows from Bleach. The factions would have to figure out how to deal with this new threat, and it could lead to some unexpected alliances.
One interesting plot twist could be the Keyblade wielders finding themselves in the world of Remnant. They might initially be confused by the Grimm and the Huntsmen system. For example, Sora could mistake a Grimm for a Heartless at first, but then realize it's a whole different kind of threat. Another could be Ruby and her team getting access to the power of the Keyblade. Ruby's scythe skills combined with Keyblade magic would make for an incredibly powerful combination. And perhaps a plot twist where the villains from both universes team up. Salem could see the power of the Heartless and use them to her advantage, while Xehanort might be interested in the power of the Maidens in RWBY.