Maybe the 'evil' Dumbledore was a future version of himself who had been corrupted by time - travel gone wrong. Harry, not fully understanding the situation, battles and defeats this future Dumbledore. This could then lead to a complex time - paradox plot where Harry has to find a way to fix the timeline and save the real Dumbledore from this fate.
In some fanfiction concepts, Harry might defeat an 'evil' Dumbledore if Dumbledore was secretly under the influence of a dark magic artifact. This could twist his good intentions and lead him to actions that Harry would oppose. Harry, with his strong sense of justice and loyalty, would then fight against this corrupted Dumbledore.
A plot twist could be that Dumbledore faked his own death to test Harry's loyalty. But when Harry starts to turn on him, Dumbledore realizes his plan backfired. This would create a lot of tension and conflict between them, and also force Harry to re - evaluate his entire relationship with Dumbledore.
A common plot could be that there's a corruption within Hogwarts that Dumbledore is unknowingly a part of. Harry, being the hero, discovers this and has to fight Dumbledore to stop it. Another plot might involve time - travel, where Harry from the future goes back and has to defeat Dumbledore to save the wizarding world from a greater threat that Dumbledore's actions in the present are causing.
One possible plot twist could be that Dumbledore was under the influence of a dark magic spell that made him kill Hagrid. And Harry, realizing this, has to find a way to break the spell and clear Dumbledore's name while also dealing with his own grief and anger over Hagrid's death.
In this kind of fanfiction, it could be that Dumbledore has some very complex motives for 'kidnapping' Harry. Maybe he wants to protect Harry from a danger that he can't explain openly. For example, there might be a powerful dark wizard who has found a way to spy on Hogwarts and Dumbledore believes that keeping Harry in a secret location is the only way to keep him safe.
It could be that after a series of events that make Harry question his own judgment, he submits to Dumbledore's authority. For instance, if there are false prophecies or misinformation floating around that lead Harry astray. Dumbledore, with his greater experience and knowledge, helps Harry see the truth. So Harry decides to submit to Dumbledore in order to get back on the right track and protect Hogwarts and the wizarding world.
In a fanfiction, Dumbledore might steal out of desperation. Suppose there was a situation where a curse was about to be unleashed on Hogwarts, and the only way to stop it was by stealing a particular ingredient for an antidote from a place where it was not supposed to be taken. Dumbledore, seeing no other option, decides to steal it. His motive here is to save the school and its students, even if it means breaking the rules.
One possible scenario is when he meets an ancient and powerful magical being that has just emerged after a long slumber. Dumbledore, in his wisdom, bows to show respect for this being's age - old magic and power. Another could be in a situation where he is facing a group of powerful wizards from a different culture with their own traditions, and he bows as a sign of diplomatic respect.
One common theme is manipulation. Writers may show Dumbledore as using Harry and others for his own secret ends. Another theme could be misinformation. They might depict Dumbledore as spreading false information to keep control. Also, power - hungry is a theme, where Dumbledore is seen as being after more power than he lets on.
Yes, there are some fanfictions that explore the idea of Dumbledore being evil. Some authors might do this to add a new and unexpected twist to the well - known story. They might question Dumbledore's actions and motives, such as his decisions regarding Harry Potter's upbringing and the way he handled the fight against Voldemort. However, this is a very different take from the original story where Dumbledore is generally seen as a wise and benevolent figure.