One interesting plot twist could be a character from 'Supernatural' getting the kagune power from 'Tokyo Ghoul'. For example, Dean suddenly having a rinkaku kagune and having to learn how to control it while still hunting demons. It would add a whole new layer to his character as he struggles with this new, inhuman power.
One interesting plot twist could be the ghouls in the Attack on Titan world. Imagine if ghouls were hidden among the titans. They could feed on the bodies of dead titans or even on the soldiers without being detected at first. Another could be the Ackermans having some sort of connection to the ghoul powers. Maybe their enhanced strength is related to a dormant ghoul gene. And a third could be the Scouts finding a way to use ghouls' kagune to fight the titans more effectively, like creating weapons out of kagune material.
A cool plot twist could be a ghoul - Titan hybrid. Imagine a Titan with the regenerative abilities of a ghoul. This would pose a whole new level of threat to the characters from both universes. Also, the idea of the ghouls' coffee being a valuable resource in the Attack on Titan world could be an interesting twist. Since coffee is so important to ghouls, it could have some unforeseen effects on the Titans or the people in that world.
In some crossovers, like the one with 'Bleach', a really creative plot twist is when Kaneki's kagune somehow gets linked to a Hollow's power. It completely changes the power dynamics and makes for some intense battles. The idea that his ghoul nature could be combined with Hollow abilities in such a way was unexpected and exciting.
Perhaps a plot twist where the Mist from Percy Jackson's world starts to affect Tokyo Ghoul. The Mist could make humans in Tokyo see ghouls as something completely different, like mythical creatures from their own Japanese folklore. This would not only change how the humans in Tokyo Ghoul react to ghouls, but also how the ghouls themselves perceive their place in the world and their relationship with humans.
Well, perhaps a major plot twist could be that the CCG (Commission of Counter Ghoul), which is supposed to be against ghouls, has been secretly working with some ghouls for their own ulterior motives. This would be a huge shock as it goes against everything they are known for. Also, there could be a twist where a ghoul's kagune (their weapon - like organ) mutates in a way that gives them an unexpected advantage or disadvantage.
One possible plot could be that Uta, with his unique mask - making skills from Tokyo Ghoul, gets involved in a situation where he has to create a special mask for a character from the Uta no Prince - sama world. Maybe this mask gives the Uta no Prince - sama character some special powers related to the ghoul world, like enhanced hearing or the ability to see in the dark. And then they have to navigate through both the music - filled world of Uta no Prince - sama and the dangerous world of Tokyo Ghoul together.
Maybe a ghoul travels forward in time and discovers that in the future, ghouls are no longer hunted because a new food source has been found. This would be a huge shock to the ghoul, who has only known a life of hiding and hunting humans. They could then try to bring this knowledge back to their own time to change things for the better.
A plot might involve a magical accident that transports some of the Tokyo Ghoul characters into the wizarding world. Kaneki could end up at Hogwarts and be sorted into a house. He'd struggle to hide his ghoul identity while also trying to find a way back home. At the same time, the wizards are intrigued by his unique abilities and some, like the more power - hungry ones, might try to use him for their own gain. Harry Potter and his friends would then have to decide whether to trust Kaneki or not.
One possible plot could be that Naruto and his friends are sent to the Tokyo Ghoul universe by some sort of space - time jutsu gone wrong. Naruto, with his strong sense of justice, would be immediately intrigued by the situation of the ghouls. He might try to find a way to co - exist between humans and ghouls, using his ninja way. He could team up with some of the more sympathetic ghouls, like Kaneki, and together they fight against the more extreme elements on both sides, whether it's the violent ghouls who only see humans as food or the humans who want to exterminate all ghouls without question.
One plot idea could be that a character from Tokyo Ghoul ends up in Ikebukuro (the setting of Durarara). For example, Kaneki could find himself in the middle of the Dollars' activities. He might initially be confused by the different kind of chaos compared to the ghoul world. Another idea is that Celty's head mystery somehow gets intertwined with the ghouls' existence. Maybe there's a ghoul who has knowledge about her head, and this leads to an alliance between Celty and some of the Tokyo Ghoul characters to find out the truth. A third plot could involve the gangs in Durarara getting involved with the ghoul - human conflict in Tokyo Ghoul. They might try to take advantage of the situation for their own gains, but end up getting more than they bargained for as they learn about the true nature of ghouls.