A really unique plot twist in DC Vampire fanfiction can be that the Green Lantern Corps has to deal with a vampire - like entity that feeds on the energy of their rings. This forces them to find new ways to power their rings and fight this entity. And sometimes, a plot twist is that a vampire version of Aquaman rules the underwater world, and the normal Aquaman has to figure out how to stop him without getting turned into a vampire himself.
One interesting plot twist could be when Naruto, as a vampire, discovers a hidden power within himself that is related to the Rosario Vampire lore in a completely unexpected way. Maybe it's a power that only activates when he's in the Rosario Vampire world and it changes the course of the story.
In some fanfictions, a major plot twist is when Goku's ki energy starts to interact in unexpected ways with the magic in the Rosario Vampire world. For example, it might accidentally trigger a long - dormant spell or power within a certain youkai. This causes chaos as both Goku and the other characters have to figure out how to deal with this new situation.
Well, perhaps a great plot twist is when Naruto discovers that the vampire transformation was part of a larger prophecy. And in order to fulfill this prophecy, he has to team up with some unlikely allies, like the vampires from a hidden clan that has been in conflict with the ninja world for ages. Also, his transformation might make some of his old enemies see him in a new light, either as a threat or as a potential ally in a new kind of power struggle.
In some fanfics, a plot twist could be that a demigod turns into a vampire. This completely changes the dynamic as they now have to deal with their new vampiric nature while still having their demigod powers. It's a really unique take on the crossover.
A really interesting plot twist is when a character from Arrow gets turned into a vampire in some fanfictions. For example, in 'The Dark Transformation', Felicity Smoak gets bitten by a vampire and has to deal with her newfound vampiric nature while still trying to help Team Arrow. It completely changes her character dynamics and adds a whole new layer of complexity to the story.
One interesting plot twist could be a character from Rosario Vampire getting transported to the Ranma universe and having to adapt to its unique martial arts and gender - changing situations. For example, Moka could end up in Furinkan High School and have to deal with Ranma's crazy antics. Another plot twist might be a fusion of the two worlds' magic systems. Maybe the nekos from Rosario Vampire learn some of Ranma's martial arts techniques and combine them with their own powers to create new and powerful attacks. A third plot twist could involve a love triangle between a character from each series and a new character created in the crossover. This would add a whole new layer of drama and conflict to the story.
A great plot twist could be the discovery that Naruto and Raven are related in some way through a long - lost multiversal connection. This would completely change their dynamic and the way they interact with each other. Also, perhaps Naruto's ability to transform into different forms gives Raven new insights into her own powers of transformation or shape - shifting. Another plot twist might be that a powerful artifact in the DC New 52 world is actually linked to Naruto's world, and only they can unlock its true potential together, leading to a race against other characters who want to use it for evil purposes.
In some fanfics, a plot twist could be that a vampire from Vampire Diaries turns out to be a long - lost relative of a Hogwarts student. This completely changes the dynamics as the student has to deal with their newfound family connection and the fact that they're a vampire.
One interesting plot twist could be that Buffy becomes a vampire but still retains some of her Slayer powers. This creates an internal struggle as she has to fight her new vampire instincts while also using her old skills. Another could be that she turns into a vampire and finds out that there's a whole new level of vampire society that she was unaware of, which changes her perspective on the whole vampire - slayer dynamic.
One interesting twist could be that the vampire breath actually transfers the consciousness of the victim into the body of a vampire for a short time. This leads to a situation where the main character experiences life as a vampire and discovers that vampires are not all bad, which completely changes their perspective on the vampire - human conflict.