Well, there could be new secrets revealed about the Hall of Prophecy. Maybe a young wizard stumbles upon a prophecy that was lost for centuries and has to figure out what to do with it.
One possibility is that the fanfic focuses on a group of students who sneak into the Department of Mysteries out of curiosity. They find themselves in the Death Chamber and have to find a way to escape the veiled figure that haunts it. Along the way, they might discover that the Department has a connection to an ancient magic that was thought to be lost, and they have to decide whether to keep it a secret or share it with the wizarding world.
It could be a young, unknown wizard who has a special gift for sensing mysteries. He or she might be drawn to the Department of Mysteries like a moth to a flame.
The most obvious torturers would be the Death Eaters. They are Voldemort's loyal followers and would do anything to please their master. If they got the chance to torture Harry in the Department of Mysteries, they would surely take it. They might want to break Harry's spirit and prove their loyalty to Voldemort.
Well, it would probably change the entire course of the story. Many characters' arcs and plotlines would be drastically different.
One possibility is that the Mandalorian's ship, the Razor Crest, could end up near Hogwarts. The students would be amazed by this strange flying machine. The Mandalorian might be searching for a lost Jedi or Sith relic that has some connection to the wizarding world. He could then get involved in the ongoing struggle against Voldemort or other dark forces in the Potter universe.
One interesting storyline could be about a new mystery uncovered within the Department of Mysteries that the original characters didn't encounter. For example, a hidden chamber filled with ancient magic that has the potential to either save or destroy the wizarding world. Another could be a story where a character gets trapped in a time - loop within the Department, reliving the same events over and over until they figure out how to break free. There could also be a fanfiction where a young, unknown wizard or witch is secretly working in the Department and discovers a plot against Hogwarts by a group of dark wizards who are using the Department's resources.
Perhaps in the fanfic, Harry is lured into a trap in the Department of Mysteries. Once there, Death Eaters could torture him to find out how he was able to resist Voldemort's attempts to possess him. They might also be interested in the connection between Harry's mind and Voldemort's, thinking that by torturing Harry they can gain some sort of power over that connection.
Well, perhaps Harry could be reporting some dark wizard activity. He might call the Department of Magical Law Enforcement (DMLE) to inform them about a Death Eater sighting. This could lead to a big investigation within the wizarding world.
One possibility is that a new prefect, who is a bit of an outsider, enters the Prefects Bathroom and discovers that the other prefects have been excluding them from some important information. This could lead to a series of events where the new prefect tries to prove themselves worthy and uncovers a plot that the other prefects were involved in, either by accident or due to some misguidance. It could be a story of self - discovery and redemption within the context of the Prefects Bathroom in the Harry Potter universe.
Well, he might start to fight for equality among the wizarding world's different social classes. He could advocate for fair treatment of house - elves, for example, trying to end their enslavement and give them equal rights like any other magical being.
Perhaps Harry discovers a long - lost magical item in one of the vaults during his apprenticeship. This item could be of great importance to the wizarding world, and he has to decide whether to keep it a secret or reveal it to the authorities. Along the way, he has to deal with the greed and envy of some of the other employees at Gringotts.