It could also be an entity that is manipulating Harry's perception of Dumbledore. For example, a dark wizard or a magical creature that has its own agenda. This entity wants to create chaos in the wizarding world by pitting Harry against Dumbledore. So, while Harry thinks he is doing the right thing by taking down Dumbledore, he is actually being used by this other antagonist.
Dumbledore himself could be seen as the main antagonist in this scenario. Since Harry is set on taking him down, Dumbledore's actions, whether they are truly malicious or just misinterpreted, would be the main obstacle for Harry to overcome.
Maybe in the fanfiction, there is a misinformation or a spell that has corrupted Dumbledore's mind. Harry, being the hero he is, notices the change in Dumbledore's behavior. He decides to take down Dumbledore because he thinks it's the only way to save the wizarding world from the new, dangerous path Dumbledore seems to be leading them on. For example, Dumbledore might be making alliances with dark forces unknowingly due to the spell, and Harry has to stop him.
I'm not sure specifically as I haven't read that exact fanfiction. But it could potentially be about Harry Potter having some sort of conflict with Dumbledore and taking actions against him. Maybe Harry discovers some dark secrets about Dumbledore that make him question his leadership and take steps to oppose him in the fan - created storyline.
The main antagonist could be a Slytherin student who has a vendetta against Harry. When they see Harry with the snake, which they believe should belong to a Slytherin, they start causing trouble for Harry. They might try to frame Harry for using dark magic with the snake or try to steal the snake to prove their superiority over Harry.
Well, in this kind of fanfiction, Dumbledore himself would be the main antagonist since the title implies that he is the one 'breaking' Harry. He would be acting against Harry's well - being and goals.
Maybe it's a dark wizard who has an interest in the snakes Harry is taking care of. He wants to use the snakes for some dark magic purposes. So he constantly tries to steal the snakes from Harry or even harm Harry to get to the snakes. For example, he could be a follower of Voldemort who believes the snakes hold some special power that can help bring back the dark lord.
It could be a dark wizard who wants to steal Harry's inheritance for his own gain.
There are several places to search for this fanfiction. Fanfiction.net is a large platform with a vast collection of Harry Potter fanfictions. Another option is Archive of Our Own. They have a great tagging system. So, when you search for 'harry potter takes dumbledore down' on either of these sites, you may be able to find the specific fanfiction you're looking for. However, not all fanfictions are on these two sites, so you might also want to check some smaller, more specialized Harry Potter fanfiction communities or forums where users might share their own works or links to other hard - to - find fanfictions.
Some of the younger students who looked up to Harry, like Neville, could support him. Neville has grown to be a strong and brave character. He might see Harry's actions as a way to make the wizarding world a better place. Also, those students who have felt wronged by Dumbledore's decisions in the past, perhaps in terms of school policies or safety, could come forward to support Harry in the court case.
One possible plot could be that Harry discovers some long - hidden secrets about Dumbledore's actions during the war. Maybe he finds out that Dumbledore knew more about Voldemort's plans but didn't act in a way Harry thought was right. So, Harry decides to take him to court to expose the truth and seek justice for those who suffered because of what he believes were Dumbledore's missteps.
Another possibility is that the antagonist is a powerful and ancient magical being that has its own agenda. This being doesn't want Harry to reach his full potential as Dumbledore hopes because it fears that a powerful Harry could disrupt the balance it has been maintaining in the magical world for centuries. So it tries to create obstacles for Dumbledore's efforts to help Harry.