In some fanfictions, there could be a plot twist where Draco and Harry find out that one of the Horcruxes has the power to control the minds of those who get too close to it. And Draco, being more attuned to the dark arts initially, is the first to be affected but then manages to resist it with Harry's help. This would add a lot of tension and drama to their Horcrux hunting adventure.
One interesting plot twist could be that Draco has some hidden knowledge about the Horcruxes from his family's dark secrets. Maybe his mother had unknowingly passed on some crucial information to him that helps Harry and him in a very unexpected way during the hunt.
Harry is brave and impulsive. His eagerness to destroy the Horcruxes quickly drives the story forward. Draco, on the other hand, is more cautious and calculating. He might slow down Harry at times, but also ensures they don't rush into dangerous situations blindly.
One interesting plot twist could be that the last Horcrux is not an object but a person no one suspected. For example, it could be a seemingly innocent bystander who has been under Voldemort's control all along without anyone realizing.
Well, in some fanfictions, a plot twist might be that Draco and Harry are forced to marry by a magical contract that was hidden for ages. And as they try to break it, they actually fall in love. Or perhaps a twist where Draco is actually a spy for the good side all along and their marriage is part of a grand plan to expose the remaining Death Eaters. There could also be a twist where Harry loses his memory and Draco has to make him fall in love with him all over again while dealing with the wizarding world's reaction to their union.
One possible plot twist could be that Draco has a hidden agenda all along. Maybe he's actually trying to protect a particular Horcrux for his own reasons. Another could be that he discovers a new Horcrux that no one else knew about, throwing the whole hunt into chaos.
In some fanfictions, a great plot twist is when Draco is on the verge of making a really bad decision, like joining the Death Eaters completely. But then he discovers his true relation to Severus. This changes his perspective as he realizes Severus has been secretly protecting him all along. It makes him question his loyalty to the Dark side. Also, there could be a plot twist where Severus has to choose between his loyalty to Dumbledore and protecting his son Draco, which creates a lot of internal conflict for him.
In some fanfictions, when Harry absorbs the Horcrux, it could lead to a moral dilemma within him. He has to struggle with the dark influence of the Horcrux while still trying to be the good wizard he is. This internal conflict can make for a really engaging story, with Harry constantly fighting his inner demons and trying to separate his own identity from that of Voldemort's.
One interesting plot twist could be that Severus and Harry are forced to marry for political reasons in the wizarding world. Maybe there's a threat from a dark force and their union is seen as a way to unite different factions. Another could be that they initially hate the idea but gradually fall in love as they discover things about each other they never knew. For example, Harry might learn about Severus's deep - seated loyalty to Dumbledore and Severus might see Harry's strength beyond his Gryffindor bravado.
A common plot twist is the discovery of a hidden prophecy that involves both Draco and Hermione. This prophecy could be related to the future of the wizarding world and forces them to put aside their differences and work together. It adds an element of mystery and urgency to the story.
Perhaps in the fanfiction, Draco Malfoy turns out to be a double agent. He pretends to be on the side of the Death Eaters like his family, but in reality, he is secretly helping Harry Potter and the Order of the Phoenix. Snape discovers this and has to decide whether to expose Draco or use his secret to their advantage. This would create a lot of tension and unexpected alliances.
One interesting plot twist could be that they discover a hidden magic that binds their fates together from a very young age. This magic makes them able to sense each other's emotions and they have to learn to deal with this new connection while still being in the rival houses at Hogwarts.