Dumbledore, even if he is dead in the original story, could play a role in some fanfictions. His wisdom and post - death influence could guide Harry on how to fake his death. Maybe he left behind some instructions or prophecies that Harry discovers and uses to his advantage. Also, the Order of the Phoenix members like Lupin or Sirius (if brought back in some way in the fanfiction) could offer their help. Lupin's werewolf abilities might be used in some creative way to create the illusion of Harry's death, and Sirius could use his Animagus form for the plan.
His best friends Hermione and Ron would be the most likely candidates. Hermione's intelligence and vast knowledge of magic could come up with a complex plan to fake Harry's death. Ron, with his loyalty and bravery, would be there to support and execute the plan. They have been through so much together that they would be willing to take such risks for Harry.
Some fanfictions might have Harry getting help from magical creatures. For example, the house - elves, known for their loyalty and powerful magic in their own right. Dobby, if he was still alive in the fanfiction, could use his unique magic to create an elaborate death - like scenario for Harry. Or perhaps the centaurs, with their knowledge of the stars and ancient magic, could assist Harry in faking his death in a way that is in harmony with the natural and magical order of things.
Hermione and Ron are the most likely candidates. Hermione's vast knowledge of magic and Ron's loyalty and combat skills would make them perfect accomplices. They could have used their combined skills to plan and execute the fake death.
Perhaps Death is a being from a different dimension in this fanfiction. It exists outside the normal rules of the wizarding world and has the power to interfere when it deems necessary. It could have its own motives for helping Harry. Maybe it wants to study the unique magic that Harry possesses, or it could be that there is a prophecy that ties Harry's success to the stability of the multiverse, and Death is simply acting to preserve the greater good.
Maybe he used some rare magical artifacts. In the wizarding world, there are many mysterious items. He could have found an artifact that allows him to project an image of his death while he actually hides in a magically protected place. It's also possible that he faked his death by making a deal with some magical creatures that are good at deception, like the house - elves. They could have used their magic to make everyone believe he was dead.
One possibility is that Harry uses some advanced and little - known magic. He could have found a spell in an ancient book in the Room of Requirement. This spell might allow him to project an image of his death while he actually hides himself in a magically protected space. He may also have made arrangements with the Order of the Phoenix to spread the news of his death convincingly.
It could be an unknown character who has been in hiding all this time. Maybe she was once a powerful witch who made a pact with death and became its representative in the wizarding world.
Dumbledore could also play a role. Even if he's not alive in the normal sense, his spirit or some form of his magic could guide Harry. He might have known about the connection between Harry and Excalibur all along and left behind some hints or instructions for Harry to follow.
Hermione could help. She's very smart and could research about the dragon's weaknesses.
Well, in this kind of fanfiction, Harry might receive some sort of otherworldly knowledge or power from Death. Maybe Death gives him the ability to see the true nature of dark magic, which helps him in his fight against Voldemort. It could also be that Death shows Harry the fates of different characters, guiding his actions to ensure the best outcome for the wizarding world.
Hermione would be a likely helper. She's smart and practical, and she could help Harry figure out what to do with all the stuff in the vaults, like how to properly inventory and distribute the items.
Perhaps Neville Longbottom could take on this role. He has shown great courage throughout the series. His experiences with loss, like the death of his parents, could lead him down a path where he becomes the apprentice of death, using his newfound powers to protect others and bring a new balance to the wizarding world.