Well, perhaps the plot twist could be related to the prophecy. If Harry looks like a girl, the Dark Lord might not recognize him as the one who can defeat him at first. This would change the whole dynamic of their encounters. Also, it could affect Harry's relationships with his friends. Hermione might be more eager to share certain things with 'female - Harry' as they would have more in common in the eyes of society. Ron, on the other hand, might struggle with his feelings as he's used to Harry being a boy. This could lead to some comical yet heart - warming moments in the fanfiction.
In this type of fanfiction, an interesting plot twist might be that Harry, as a girl, is underestimated by many of the male characters at first. But then she uses this to her advantage. She could pretend to be meek and mild while secretly gathering information and planning strategies. Also, her transformation could lead to a change in the way Hogwarts is run. Maybe she starts a movement for more equality between male and female students, which causes a stir among the old - fashioned teachers.
One idea could be that Harry's new appearance as a girl causes a stir at Hogwarts. His friends are initially shocked but then accept him as always. Another could be that he uses this new look to his advantage when it comes to spying on the Death Eaters, as they don't recognize him. Maybe he even gets to experience the wizarding world from a different perspective as a girl, like how people interact with him differently in social situations.
Perhaps a plot twist could be that the magical creatures interact with Harry differently. In the original, they had a certain way of relating to him, but in this fanfiction, being raised as a black wizard might make some creatures more or less friendly towards him. Some might see him as a symbol of change in the wizarding world and be more drawn to him, while others might be suspicious. Also, the way Harry approaches magic could be different. He might draw on cultural magic that is unique to his black heritage, which could give him an edge in certain situations or make him a target for those who fear change.
Well, one possible plot twist could be a revelation about a character's true heritage that was hidden all along. For example, a minor character might turn out to be related to one of the major wizarding families in ways no one expected.
One possible plot twist could be that as a girl, Harry has an even stronger connection to magic related to femininity, like a special bond with female magical creatures. Another could be that she faces different social challenges in the wizarding world, perhaps more pressure to conform to traditional female roles while still being a hero.
One plot twist could be that the maze reveals different illusions for each contestant based on their deepest fears. For example, Harry could see Voldemort killing his friends instead of the normal obstacles. Another could be that the cup at the end is a fake and leads to a more dangerous trial. Or perhaps one of the other champions teams up with a dark wizard within the maze to try and eliminate Harry.
Perhaps Lucifer is actually an ancient dark wizard who was banished long ago and is now trying to return using the chaos of the wizarding war in Harry Potter's time. He could manipulate events from the shadows, and Harry, with the help of Dumbledore's portraits (which have some ethereal knowledge), figures out Lucifer's true identity and purpose, leading to a showdown that combines magic from both universes.
Maybe Harry would have a different view on the wizarding world. Growing up with the Delacours, he'd be exposed to a more international magical community from a young age. So, instead of being so focused on the British wizarding world's problems like Voldemort, he might be more interested in international magical relations and how to unite different magical cultures.
Maybe Harry's parents are alive but they've been working undercover for a long time against a different dark force that is allied with Voldemort. When they come back into Harry's life, they bring with them a whole new set of problems and mysteries. For example, they might have made some dangerous pacts with other magical beings in order to gain information. Harry has to deal with the consequences of these pacts while also trying to keep his family together. Another plot twist could be that they are alive but time - traveling is involved. They've been stuck in a different time period and Harry has to figure out how to bring them back to the present, all while Voldemort is still a threat.
One interesting plot twist could be that Harry discovers he has the ability to communicate with the Basilisk on a deeper level than just Parseltongue. Maybe he can see through the Basilisk's eyes and use this to his advantage in uncovering secrets within Hogwarts that even Dumbledore doesn't know. Another could be that the Basilisk is not truly a villain but was being controlled by a dark force all along, and Harry has to find a way to break that control and free the Basilisk.