Another possible plot twist is that the Deathly Hallows are fakes all along, and Hermione is the one to figure it out. It could be that a powerful dark wizard has been manipulating everyone by creating false Hallows to create chaos and gain power. Hermione's discovery of this would turn the wizarding world's understanding of the Hallows upside down and force them to find a new way to defeat Voldemort.
One interesting plot twist could be Hermione discovering a hidden power within herself related to the Deathly Hallows. Maybe she finds out that she has a special connection to the Elder Wand that no one suspected before.
In some fanfics, a plot twist could be that Hermione actually uncovers a long - forgotten prophecy about the Deathly Hallows that changes the whole course of the fight against Voldemort. For example, it might reveal that the true power of the Hallows lies not in their individual use but in a combined ritual that only Hermione can perform. This would completely shift the power dynamics and the strategies of the good side in the battle.
One interesting plot twist could be that a minor character from the original series turns out to be a key player in the fanfic. For example, a Hogwarts student who was barely noticed before might be revealed as a Death Eater spy all along, adding a whole new layer of mystery and danger to the story.
One interesting plot point could be an alternate take on their relationship during the Horcrux hunt. Maybe in the fanfic, they face a particularly difficult Horcrux that tests their bond in a new way, like a Horcrux that plays on their insecurities about each other.
Some fanfictions have a plot twist where the Deathly Hallows are actually a test set by the original founders of Hogwarts. Harry finds out that the real purpose of the Hallows was not just to defeat Voldemort but to bring about a new era of magic in the wizarding world. Another plot twist could be that Snape was not actually killed by Nagini but was in a magically induced coma and wakes up at a crucial moment to help Harry. Additionally, a fanfiction might have a twist where the Horcruxes have a connection to the Deathly Hallows, and by destroying the Horcruxes in a certain order, Harry gains new powers related to the Hallows.
Well, Harry Potter would most likely be one of the main characters. He is an important part of the original story and would surely play a significant role in the fanfic as well.
A really cool plot twist in some fanfictions is that Harry actually has a long - lost sister. This sister could be hidden away by some powerful magic for her protection. Her appearance in the Deathly Hallows time frame would throw everything into chaos as she might have her own ideas about how to deal with Voldemort and the Deathly Hallows.
A really out - there plot twist in fanfiction could be that the Deathly Hallows themselves have a different origin or purpose than what was originally thought. For example, the Elder Wand might be a key to a whole new realm of magic that Voldemort was unaware of, and Harry uses this knowledge to his advantage in the battle against the Dark Lord.
Well, sometimes the fanfictions might have a plot twist where the Deathly Hallows themselves have different powers than what was originally thought. Maybe the Elder Wand has the power to not only be unbeatable in duels but also to reverse the effects of dark magic, which completely changes the dynamic of the story. This could lead to a situation where characters who were previously doomed by dark magic curses are suddenly cured, and it alters the relationships between the different factions in the wizarding world.
One interesting plot twist could be that a minor character from Hogwarts, like Neville, discovers a hidden power within the Deathly Hallows that was previously unknown. Maybe he realizes that the Elder Wand has the ability to not only transfer power through combat but also through acts of self - sacrifice, which completely changes the way everyone views the power of the Hallows.
One interesting plot twist could be that Hermione discovers a hidden spell within the Goblet of Fire that no one else knew about. This spell could change the nature of the Triwizard Tournament in unexpected ways.
One interesting plot twist could be that Hermione discovers she's the Heir of Stone not through traditional means but during a dangerous encounter with a dark wizard. The wizard tries to use her for some evil purpose related to the power of the Stone, but she manages to turn the tables on him.