The fanfiction could focus on Dumbledore's backstory. Fans might write about his early years at Hogwarts as a student, his friendships, and how he developed into the great wizard he became. It could also include his interactions with other magical creatures in more depth than the original series, such as having secret meetings with centaurs or merpeople to gain wisdom.
One possible plot could be that Dumbledore is framed for a crime he didn't commit. Maybe there's a dark wizard who has managed to plant false evidence against him. For example, evidence that he was involved in some sort of dark magic plot. Another could be that the Ministry of Magic, fearing his power and influence, decides to arrest him on false pretenses to gain more control over Hogwarts. This could lead to a lot of chaos in the wizarding world as Dumbledore has many allies and supporters who would not stand for his unjust arrest.
In such a fanfiction, Dumbledore might face consequences for his actions. For example, his manipulative ways could be exposed. Maybe his secrets regarding Harry Potter's upbringing and the true purpose behind his actions could come to light, leading to a loss of his respected status among the wizarding community.
Well, it could be that Rumple discovers some past wrong Dumbledore did to him or his kind. Maybe Dumbledore once meddled in Rumple's magical affairs and now Rumple wants to make him pay. He could start by using his unique magic to create chaos in Hogwarts, like making the staircases go haywire or the portraits misbehave.
Well, perhaps in the fanfiction, Dumbledore is arrested because of his ties to a certain group that the Ministry has deemed as a threat. For example, he might have been secretly helping a group of werewolves or half - bloods who are fighting for equal rights, and the prejudiced Ministry decides to arrest him to stop what they see as a subversive movement. This could lead to a great uprising within the wizarding community, with students and other professors trying to prove his innocence.
In a 'Harry Potter gets revenge on Dumbledore' fanfiction, Harry could find out that Dumbledore knew about certain threats to his life but didn't do enough to protect him. So, Harry decides to get revenge by undermining Dumbledore's influence at Hogwarts. He might start by convincing the other students that Dumbledore isn't as infallible as they thought. He could do this by revealing some of Dumbledore's past mistakes. Then, he could work on getting the school governors to question Dumbledore's leadership, gradually chipping away at his power and status within the wizarding community.
One possibility is that Dumbledore gets caught spying on a group of Death Eaters. This would put him in a very dangerous situation as the Death Eaters are extremely cruel and loyal to Voldemort. He might be tortured for information about the Order of the Phoenix. However, Dumbledore is very resourceful and would probably be able to hold his own against them for a while, giving his allies time to figure out a rescue plan.
Aspiring young writers who are fans of the magical world. They see Dumbledore as a rich character to base their fanfiction on. They could be students who are inspired by the detailed world of Hogwarts and want to contribute their own ideas about Dumbledore through writing.
Maybe Harry discovers a new spell that Dumbledore is unaware of and uses it to outwit him. For example, a spell that can reverse time briefly in a small area, allowing Harry to redo a crucial moment in their 'game' to his advantage.
In some interpretations, one possible crime could be his manipulation of Harry Potter. He knew Harry was a tool to defeat Voldemort from the start and perhaps didn't fully disclose this to Harry, leading Harry into a dangerous life without his full knowledge.
There's also a chance that Dumbledore gets caught by a group of rogue magical creatures. For instance, if he was exploring an area that was supposed to be off - limits to wizards and the creatures there saw him as an intruder. They might not be as rational as wizards and could hold him captive without really understanding who he is.