Who could be the main antagonist in a 'Harry Potter Master of Death' original fanfiction?

Perhaps a dark wizard who is jealous of Harry's new power. This wizard could be someone who has long been in the shadows, waiting for the right moment to strike. He might see Harry as a threat to his own plans of taking over the wizarding world.

It could be Voldemort who somehow follows Harry into the Pokemon world. He might try to use the power of Pokemon to regain his strength and take over both the wizarding world and the Pokemon world. His dark magic could corrupt some of the Pokemon, turning them into his minions.

It could be Voldemort who somehow follows Harry into the DC universe and teams up with some of the DC villains like Lex Luthor. Their combined evil intellect and power could pose a great threat to both Harry and the DC heroes.

It could be Voldemort who somehow manages to extend his reach into the ROTG world. Since Harry is the master of death, Voldemort might see this as an opportunity to gain even more power and immortality. He could team up with some of the villains from ROTG, like Pitch, to create chaos and try to defeat Harry once and for all.

Perhaps an ancient spirit that has been awakened by the imbalance in the life - death cycle due to Harry becoming the Master of Death. This spirit sees Harry as the cause of the chaos and tries to destroy him to restore the balance in a way that is harmful to the wizarding world.

Perhaps an old follower of Voldemort who was in hiding. This person finds out about the Eyes of Death and believes that with their power, he can bring back Voldemort's legacy even stronger. He becomes the main force against Harry and his friends throughout the fanfiction.

It could be Voldemort again, but in a more powerful and death - centered form. Maybe he has found a way to fully embrace the power of death and become an even greater threat. Since Harry is the champion of death, it would be a battle of two opposing forces related to death.

It could be Voldemort still. Even if Harry becomes associated with death, Voldemort is the ultimate symbol of death and destruction in the wizarding world. Their battle could take on a new dimension as Harry now has a different relationship with death.

The main antagonist could be Master. Since the title mentions Master, it's likely that this character has a lot of power and influence in the merchant world. They might be using their position to cause harm or manipulate things in a way that leads to death, which would make them a natural antagonist for Harry and Tony to oppose.

Well, perhaps the fanfiction could focus on Harry's internal struggle with being the Master of Death. He might feel isolated as no one truly understands the power he holds. So, he embarks on a journey to find others who have had similar experiences in the past. Along the way, he discovers secrets about the founders of Hogwarts and how they were also connected to the concept of the Master of Death in ways not previously known.