An old enemy of the Black family who resurfaces because of Cassiopeia's new - found alliance with Harry. This antagonist could hold a grudge against the Blacks for past events and see their partnership as a threat to his own plans for the wizarding world.
A powerful dark wizard who wants to use Cassiopeia's connection to the Black family for his own evil purposes. He might try to force her to give up secrets or artifacts related to the family, and when she refuses, he targets both her and Harry.
In some fanfictions, Cassiopeia Black is significant because she may have a role in changing the course of the wizarding world. Maybe she discovers a new form of magic or uncovers a plot against the wizarding community that she then has to fight against. Her character gives fanfiction writers the opportunity to expand on the existing Harry Potter universe in unique and creative ways.
Cassiopeia Black is an interesting figure in Harry Potter fanfiction. She could be portrayed in various ways. Some fanfictions might depict her as a powerful witch from the Black family heritage, with a complex personality influenced by the family's pure - blood mania and dark magic tendencies. However, in many cases, she remains a somewhat mysterious character, with her actions and relationships being re - imagined by different fanfiction authors.
Maybe it's a group of dark wizards who believe in a more extreme form of pure - blood ideology. They see Arcturus Black as a traitor for teaming up with Harry Potter, who is a half - blood. They plot to take over the wizarding world and eliminate anyone who doesn't fit their idea of a pure - blood wizard.
It could be Bellatrix Lestrange. Since she is a Death Eater and has a personal vendetta against Sirius, she would be a great antagonist. She might try to kill Sirius again and also target Harry to please Voldemort.
Perhaps a long - lost relative of the Potter family who feels they were unjustly excluded from inheriting the manor. This relative could be jealous of Harry's status and the wealth associated with the manor. They might use dark magic to try and claim what they think is rightfully theirs, leading to a battle of magic and loyalty within the Potter family and among Harry's friends.
A new dark wizard or witch could be created specifically for this fanfiction. This character could be interested in using the Huntsman's skills for their own evil purposes. If the Huntsman refuses, they become enemies. This antagonist could have powers related to dark forest magic, something that the Huntsman is familiar with but in a more malevolent form.
Voldemort could still be the main antagonist. Even if Demetri has some sort of connection or change in the fanfiction, Voldemort's overarching evil plans would still be a major threat to both Harry and Demetri, especially if Demetri tries to deviate from the Death Eaters' path.
The minotaur itself could be the main antagonist. It's a powerful and dangerous creature, and if it's been set loose in Hogwarts or is guarding something that Harry needs, it would be a major obstacle for him to overcome.
The main antagonist could be a dark wizard who has made the graveyard his lair. He uses the dark energy from the tombstones and the restless spirits there to power his dark magic. Harry stumbles upon this wizard's activities and has to stop him.
A new dark wizard or witch could be the main antagonist. This character, jealous of Harry's fame and power, creates a situation where Harry is framed for a heinous crime. They then ensure his arrest so that they can take over the role of the 'chosen one' in the eyes of the wizarding public and start spreading their own brand of dark magic.