In some fanfictions, a great plot twist is that the 'Prince of Slytherin' is not who everyone thinks he is. He might be under a powerful charm or disguise. And when the real identity is revealed, it turns out to be someone who has been working undercover for Dumbledore all along, which shocks both the characters in the story and the readers.
Perhaps a major plot twist is that the 'Prince of Slytherin' has a secret connection to Harry Potter. For example, they could be long - lost relatives. This would completely change the dynamic between Harry and the Slytherin character and lead to unexpected alliances and conflicts in the fanfic.
One interesting plot twist could be that Harry, in joining Slytherin, discovers a long - hidden family connection to one of the prominent Slytherin families. This changes his perception of his own identity and makes him question his place in the wizarding world.
A really cool plot twist could be that the Bound Prince was cursed by an ancient magic long ago, and the only way to break the curse is for Harry to sacrifice something precious to him, like his invisibility cloak. This creates a moral dilemma for Harry and also throws a wrench in his usual problem - solving methods, making for a very engaging story line.
One interesting plotline could be the exploration of the Slytherin Prince's backstory. Maybe he has a hidden family legacy or a past encounter that shaped his personality. Another could be his relationships within Slytherin house, like rivalries or unexpected friendships. Also, his interactions with Harry Potter in a different light than in the original books, perhaps as an ally in some situations rather than an enemy.
In certain fanfictions, a plot twist could be that the Half - Blood Prince was not a single person but a group of wizards working together. They had been leaving the notes in the potions book for a greater purpose. Another interesting plot twist might be that the Half - Blood Prince was actually an animagus and could transform into a creature that had a special connection to Voldemort's Horcruxes. This would add a whole new layer to the story. Also, there could be a plot twist where the relationship between Harry and Snape is completely different from the start. Snape is actually trying to protect Harry in a much more obvious way, but Harry misinterprets his actions because of the false reputation Snape has in the fanfiction world.
In some fanfictions, a great plot twist is that Harry himself has some hidden powers that are awakened during his sixth year. For example, he might gain the ability to communicate with magical creatures in a much deeper way. This could lead him to discover secrets about Hogwarts that even Dumbledore didn't know. And perhaps the relationship between the Half - Blood Prince and a long - lost relative of Harry's is revealed, which throws a whole new light on his family history and his role in the wizarding world.
One interesting plot twist could be that Harry, being in Slytherin, forms an unexpected alliance with Draco Malfoy. Instead of the typical rivalry, they team up to uncover a dark secret within the Slytherin house that threatens the whole school. This changes the dynamic of the story as they have to work together despite their differences.
A major plot change could be the way Hogwarts as a whole views Harry. In the original story, Gryffindor - related characters and events are often in the spotlight. But if Harry is the Prince of Slytherin, Slytherin - related storylines would be emphasized. He might be involved in Slytherin - specific secrets and politics. His battles might be more about proving himself to the Slytherin house rather than just the overall fight against Voldemort. And his interactions with Slytherin students like Draco would be far more complex, potentially evolving from enmity to some sort of alliance or at least a more nuanced relationship.
One interesting plot could be Harry struggling to fit in with the Slytherin ideals at first. He might be constantly at odds with some of the more traditional Slytherin values like pure - blood supremacy. But then he could gradually change the house from within, making his Slytherin peers see that not all Gryffindor traits are bad and vice versa.
There are various plot ideas. Some fanfictions might explore the idea that the heir of Slytherin is not a single individual but a group of people who have been secretly working to change the reputation of Slytherin house. They could be working against dark wizards within the house who are trying to revive the old ways of pure - blood elitism. Or perhaps the heir has a connection to an ancient magic that is tied to Hogwarts itself, and in order to save the school from a new danger, they must unlock this magic. It could also be a story where the heir is in a love triangle with a Gryffindor and a Hufflepuff, adding a romantic element to the plot while still dealing with the challenges of being the heir of Slytherin.