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, perhaps the Black family's dark magic artifacts play a huge role. Harry could be exposed to them at a young age. He might start to show an aptitude for certain types of dark magic not seen in the regular series. But then he has to struggle with whether to embrace this power or reject it, knowing it goes against what Dumbledore and others would expect.
One possible plot twist could be that Dorea Black, being from a pure - blood family, tries to shield Fem Harry from the growing dark forces in a different way than the Dursleys did in the original story. Maybe she uses her family's old magic and connections to give Fem Harry a more magical - centered upbringing, which leads to Fem Harry having a different set of skills and knowledge earlier on.
One possible plot twist could be that Sirius Black, being a wanted man, has to constantly move with Harry to avoid capture. This would make Harry's childhood very different from the one at the Dursleys. He'd grow up learning about the wizarding world on the run, perhaps meeting some unique characters in hiding places.
One possible plot twist could be that Dorea Black, being a pure - blooded Black, tries to instill in Harry a strong sense of pure - blood pride in a different way than the Malfoys. Instead of the usual haughty and discriminatory way, she teaches him about the history and magic of their bloodline in a more positive light. This could lead to Harry having a different perspective on the wizarding world's social hierarchy.
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.
Well, a really interesting plot twist could be his relationship with the other Hogwarts houses. He might not have the same automatic connection with Gryffindor. Instead, he could be more inclined towards Slytherin values, which would completely change his dynamic with Ron and Hermione. Maybe he would form closer friendships with Slytherin students right from the start. Also, his views on pure - blood supremacy could be more complex as he is raised in a family that might have some traditional views on blood purity.
Well, perhaps the nuns are in cahoots with some magical creatures. They could be working with a group of centaurs who have prophesied that Harry must be raised in seclusion among the nuns to gain a certain kind of purity of spirit. Then, when Harry finally enters the wizarding world, he has an aura about him that both attracts and confounds the dark forces. He might also have a special connection to the magical animals due to his time with the nuns, like being able to communicate with them on a deeper level, which would be really useful in his battles against the dark side.
A really interesting plot twist could be that the phoenix, being a symbol of rebirth, has the ability to make Harry remember his past lives. This would give him an edge as he could draw on the knowledge and skills from his previous existences. He might remember spells and strategies that were long forgotten, which would completely change the course of his fight against the dark forces.
One possible plot twist could be that Harry has unique magical abilities related to the ocean. For example, he might be able to communicate with sea creatures, which could help him in his adventures. Maybe he discovers a hidden underwater wizarding community that has been isolated from the rest of the wizarding world for centuries. Another twist could be that his enemies, like Voldemort, have a hard time reaching him in the ocean, but they find a way to use the ocean's power against him in some unexpected manner.
One possible plot twist could be that the goblins have their own motives for raising Harry. Maybe they see him as a key to some hidden treasure or power. They could be training him in secret goblin magic that no human wizard knows about.