Who could be the main antagonist in a 'Harry Potter goes to jail' fanfiction?

It could be a new character, perhaps a corrupt wizard in the Ministry of Magic who has a vendetta against the Dursleys for some reason. This wizard might make their time in jail even more difficult by withholding basic rights or subjecting them to unfair treatment. And he might be doing all this for his own gain, like trying to steal the Dursleys' Muggle money or something.

The Joker could be the main antagonist. Even though Batman is in jail, the Joker could find a way to continue his chaos - making. He might try to get into the prison to torment Batman or use the situation to his advantage by causing mayhem in Gotham City without Batman there to stop him.

It could be Danzo. He's always been a bit of a shady character in the Naruto series. He might see Naruto as a threat to his power and influence in the village. So, he could frame Naruto for some crime and get him sent to jail just to eliminate his competition.

The Kingpin could be a likely antagonist. He has the resources and the motive to frame Spider Man and get him out of the way. He could use his criminal connections to plant false evidence and make sure Spider Man ends up in jail.

It could be a new dark wizard who has some personal vendetta against Harry. Maybe this wizard has a grudge because Harry defeated Voldemort and he wants to prove he's more powerful, which enrages Harry and causes him to go on a rampage.

It could be a new dark wizard who has the power to manipulate minds. This wizard might target Harry specifically, driving him insane as part of a larger plan to take over the wizarding world. Since Harry is seen as a hero, if he goes insane, it would create chaos and make it easier for the antagonist to achieve his goals.

There could be a dark entity that lurks within the Durmstrang castle itself. It might have been awakened by Harry's arrival or has some connection to the school's past. This entity could manipulate students and teachers alike to create chaos and oppose Harry.

In a 'Harry Potter goes to jail' fanfiction, perhaps Harry breaks a new law that the Ministry of Magic has created to maintain control. For example, if he tries to teach magic to non - magic people in an attempt to prepare them for a potential dark wizard threat. The Ministry, fearing chaos, throws him in jail. Inside, he meets other wrongly - imprisoned wizards and they plan an escape together while also fighting against the unjust system.

Another possibility is that an evil wizard from the past, who was previously defeated, gets resurrected or empowered by Harry's time - traveling interference. This wizard could then become the main antagonist, using Harry's actions to their advantage and wreaking havoc on the wizarding world.

There might be a character who is secretly from the wizarding world but has turned to the dark side. This character could be after Harry in the Ouran setting, trying to use the chaos of the new environment to their advantage to get to Harry without being noticed by the Hogwarts professors.