Obviously, Harry Potter himself is one of the most common. Then there's Dumbledore who often plays a role, either as a supporter or as someone with a complex plan. Hermione is also common as she uses her intelligence to help Harry in the trial.
Obviously, Harry Potter is a key character. He is the one on trial, so the whole story revolves around him trying to prove his innocence.
Well, in some fanfictions, a plot twist could be that a character thought to be on Harry's side in the Wizengamot trial actually has a hidden agenda. Maybe they are being blackmailed by Voldemort's supporters. Also, it could be that the magical creatures of Hogwarts, like the house - elves, come forward with evidence that no one expected, which completely turns the trial around. For example, they might have witnessed something crucial that the wizards overlooked.
In some Harry Trial fanfiction, the Ministry of Magic officials are common characters. For instance, Fudge or Scrimgeour might be involved in the trial as the prosecutors or judges. Their actions and decisions can greatly influence the outcome of Harry's trial, and their motives might not always be as straightforward as they seem.
In some fanfics, there could be a plot twist where the Wizengamot itself is under the influence of a spell. So, the whole trial is a setup not just for Harry but for a larger scheme to undermine the Ministry of Magic. This would mean that Harry has to not only prove his innocence but also expose the real threat to the wizarding world.
Well, if the trial is about a Hogwarts student who is in trouble, then Neville could be one of the main characters. Or if it's a trial related to the dark side, Draco Malfoy could play a significant role. It's also possible that some minor characters from the original books, like Luna Lovegood, could become main characters in this fanfiction if they are somehow closely related to the trial, for example, if they have crucial evidence or are the ones being accused.
He might face political intrigue. There are likely those in the Wizengamot who oppose him due to his past actions and his association with Dumbledore. Also, he has to deal with the complex and often archaic laws and traditions of the wizarding world which could be a huge obstacle.
Hermione would likely be one of his allies. She's intelligent and has a strong sense of justice, always having been interested in the rights and wrongs of the wizarding laws. She could provide Harry with valuable research and advice.
Hermione Granger might also be a main character. Her intelligence would be very useful in a smart trial scenario. She could be using her vast knowledge of magic and books to help someone during the trial.
In a 'harry potter veritaserum trial fanfiction', we might see Harry as the main character, especially if he is the one on trial. Hermione would likely be there to use her intelligence to figure out any legal loopholes or problems with the use of Veritaserum. Ron would be by their side for support. Additionally, Dumbledore or other Hogwarts professors could also be main characters, perhaps acting as advisors or having some hidden knowledge about the trial and the potion.
Well, in some fanfictions, Harry might gain control over the Wizengamot through his heroic deeds. For example, if he saves the wizarding world from a great threat again, the public support could be so strong that he can influence the Wizengamot's decisions. He could also use his knowledge of magic, especially some ancient or powerful magic that gives him an edge in the political arena of the wizarding world.