Perhaps a really unexpected plot twist is that Oc is actually a double agent. He pretends to be on Joker's side, but in reality, he is working for a secret organization that wants to use Joker as a pawn in a much larger scheme. So, he has to balance his loyalty to his 'brother' and his mission for this organization, all while trying not to get caught by either side.
One interesting plot twist could be that Oc, being Joker's brother, has a completely different moral compass. Instead of chaos, he might be striving for justice in a really messed - up Gotham. Maybe he starts off as an ally to Batman, secretly feeding him information about Joker's next moves. This would turn the whole dynamic of the Batman - Joker relationship on its head.
The character Oc can be developed by exploring his backstory. Maybe he had a different upbringing than Joker, which led him to have different values. For instance, if he was sent away to a boarding school while Joker was left behind in a tough neighborhood, this could shape his more refined and moral personality.
One interesting plot twist could be that the OC babysitter has a hidden power or ability that is related to the Naruto universe. For example, she might be able to control a special type of chakra that no one knew about. Another twist could be that Naruto discovers that the OC is actually related to an important figure in the Naruto world in some way, like a long - lost relative of a great ninja. And a third plot twist might be that the babysitting job is actually a cover for a secret mission, and Naruto and the OC end up getting involved in something much bigger than they expected.
A possible plot twist could be that Hermione is a half - veela. This is not related to being a Muggleborn at all. The fanfiction could show how her veela heritage affects her magic and her relationships at Hogwarts. For example, it might make her more alluring and powerful in certain types of magic, like charms. This would completely change the way her character is typically portrayed in the original stories where she was thought to be a Muggleborn.
One interesting plot twist could be that Hermione, as a Gryffindor in the original series, starts to question the values of her own house because of her newfound admiration for Slytherin. Maybe she discovers a long - lost family connection to a Slytherin family, which makes her more empathetic towards their ways. Another could be that she uses Slytherin - like cunning to solve a problem that Gryffindor bravado couldn't handle, causing a rift between her and some of her Gryffindor friends.
One interesting plot twist could be that the kidnapper turns out to be someone Stiles thought was a friend all along. Maybe it was a werewolf in disguise who had a hidden agenda against Stiles or his friends. Another could be that Stiles discovers he has some hidden power during the kidnapping that helps him either escape or turn the tables on his captors. For example, he might find out he can communicate with spirits who guide him to safety.
One interesting plot twist could be that the kidnapped character turns out to have a hidden ability or identity. For example, a seemingly ordinary rabbit is actually a key figure in an ancient prophecy related to Zootopia. Another twist might be that the kidnapper has a noble, though misguided, reason for the kidnapping, like trying to protect the city from a threat they wrongly believe the kidnapped character is associated with. And sometimes, the kidnapped character might be kidnapped by someone they thought was a friend, adding a layer of betrayal to the story.
In these fanfictions, a possible plot twist is that the person who kidnaps Gaara is actually being controlled by a greater evil force. Gaara initially believes it's just a simple kidnapping for ransom or revenge, but as he tries to escape, he discovers the real mastermind behind it all. Another plot twist could be that Gaara is kidnapped and taken to a place that is supposed to be a haven for outcasts like him, but it turns out to be a trap. Or, the kidnapper is a time - traveler who wants to change Gaara's future by taking him out of his current timeline, which leads to all sorts of chaos when Gaara's friends try to bring him back.
One interesting plot twist could be that Hermione's real family is a powerful wizarding dynasty in hiding. For example, they might have been in hiding from a dark wizard who was after their unique magical abilities. Another could be that she was adopted to protect her from a prophecy related to her future powers. Maybe she discovers that she has a connection to an ancient magical artifact that only her real family knew about, and this discovery changes her whole perspective on her identity and place in the wizarding world.
In some fanfictions, the OC is betrayed by the entire group they thought they belonged to. This could be a club or a team within the Highschool DxD universe. The group might turn on the OC because they see the OC as a threat to their status quo. Maybe the OC has powers that the group fears will disrupt their power balance. This kind of betrayal can lead to the OC having to find new allies or even go it alone, which can be a great opportunity for character development.
A great plot twist could be that the gods of both worlds had a secret plan all along. They made Percy and Thor brothers to create a bridge between the Greek and Norse realms. But when Percy and Thor start to figure this out, they face opposition from some of the more traditional gods who don't want the two worlds to mix. This could lead to a conflict where Percy and Thor have to fight not only against external enemies but also against their own godly families. It would add a whole new layer of drama to the fanfiction.