Perhaps Harry discovers that Crowley has been raising him for a specific purpose related to some ancient prophecy. Maybe Crowley wants to use Harry to gain power in the wizarding world or even in the larger supernatural realm. This would put Harry in a difficult position as he has to decide whether to go along with Crowley's plans or break free and fight against him.
One possible plot twist could be that Harry, under Crowley's influence, starts to question the traditional concepts of good and evil in the wizarding world. He might be exposed to dark magic in a different light, not as something purely evil but as a tool with its own uses. This could lead to conflicts with his friends from Hogwarts who adhere to the more conventional views.
A plot twist could be related to Fem Harry Potter's magical abilities. Since she is raised by Crowley, she might develop some unique magical skills that are a blend of wizarding magic and Crowley's own brand of 'power'. This could make her a target for various groups in the wizarding world who either want to use her for their own gains or are afraid of her new - found powers. Also, Crowley might have some enemies in the wizarding world that he has never revealed to Fem Harry Potter. When these enemies discover her existence, they target her to get back at Crowley, putting her in great danger and forcing her to rely on skills and knowledge she has learned from Crowley to survive.
One possible main plot twist could be that Sirius manages to completely hide Harry from the wizarding world's prying eyes until he comes of age. This would mean Harry grows up without the constant threat of Voldemort's followers finding him. Another twist could be that Sirius discovers some long - hidden magic within Harry that was dormant because of his upbringing with the Dursleys, but flourishes under Sirius's care.
One possible plot twist could be that Amelia Bones, being a highly respected figure in the wizarding world, has a secret past that somehow affects Harry's journey. Maybe she was involved in some sort of pre - Voldemort plot that resurfaces when she takes in Harry. This could lead to Harry having to deal with new enemies and allies that are related to Amelia's past.
The plot could take a turn where Pan Son is initially thought to be a normal Muggle, but as he grows up with Harry, it's revealed that he has a dormant wizarding bloodline. This discovery could come at a crucial time, like when Harry is facing a great threat. Pan Son's newfound magic could be the key to turning the tide. They would then have to train Pan Son quickly and figure out how to integrate his magic into their fight against the dark side.
One possible plot twist could be that Harry, under Bellatrix's influence, becomes a much darker and more ruthless wizard. Bellatrix might train him in the Dark Arts, and he could end up being a sort of anti - hero. He might have a completely different view of the wizarding world and be at odds with his former friends from Hogwarts.
One possible plot twist could be that Ariel, while being raised by Ursula, discovers a hidden power within herself that Ursula was trying to keep dormant. Maybe it's a special kind of magic that can break Ursula's control over the sea creatures. This would lead to a power struggle between them as Ursula tries to regain control and Ariel fights for her new - found freedom and the rights of the underwater world.
A really interesting plot twist could be that Zabuza has a hidden past or connection to Naruto's family. For instance, perhaps he knew Naruto's father in a different context than what was previously known. This could change Naruto's whole perspective on his family and his place in the ninja world. Or, Zabuza could have been given a secret mission long ago related to Naruto that he never fully completed, and now raising Naruto becomes a way to fulfill that mission. This would add a whole new layer of mystery and depth to the fanfic.
Perhaps a plot twist could involve Dionysus having a secret reason for raising Percy. It might turn out that Percy is part of some grand prophecy that only Dionysus knows about, and he's been grooming Percy for a specific task that will change the fate of the gods and demigods alike. This could lead to Percy having to make some really tough choices between his loyalty to Dionysus and his friends at Camp Half - Blood.
One possible plot twist could be that Naruto develops unique jutsu influenced by Yugito's Nibi powers. Since Yugito is a jinchuriki, she might teach Naruto some special techniques related to chakra control and dealing with tailed beasts. For example, Naruto could learn a new form of Rasengan that incorporates some of the Nibi's chakra nature.
Another plot twist could be that Bellatrix realizes she has created a powerful adversary in Harry. As she raises him to be Lord Black, she instills in him a sense of power and ambition. But Harry uses that power not for the dark purposes she intended. Instead, he decides to reform the Black family traditions and bring a new era of inclusiveness to the wizarding world.