It could be a dark wizard who also has an ability related to metal. He wants to take Harry's power for himself and rule the wizarding world. For instance, he might be able to corrupt the metal in Hogwarts and turn it against the students.
The main antagonist could be a powerful magical being from another dimension who is drawn to Harry's power over metal. This being wants to use the power to open portals between dimensions and bring chaos to the wizarding world. Harry would have to use his wits and his new power to stop this being.
Maybe it's a group of Death Eaters who see Harry's new power as a threat. They would try to stop him at all costs. They could use their dark magic to counter Harry's metal - controlling ability, like creating anti - metal spells.
It could be a dark wizard who also wants to control the zombies but for evil purposes. Maybe a long - lost relative of Voldemort who has emerged from the shadows and sees the zombies as a means to finally take over the wizarding world. He might try to steal Harry's method of controlling them or create more powerful zombies that are immune to Harry's control.
Maybe Harry discovers a new spell that allows him to control metal. He could use this power to defend Hogwarts. For example, he might be able to manipulate the metal gates to keep out dark wizards.
Obviously, Harry Potter is the main character as the title implies. He's the one with the power to control the elements. Hermione Granger and Ron Weasley would also likely be important characters. Hermione could be helping Harry research about the origin of his element - controlling ability, and Ron would be by his side in his adventures, providing support and some comic relief.
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.
The main character is Harry Potter. However, other characters like Luna Lovegood could be important. Her unique perspective on the wizarding world might offer Harry new insights on how to use his reality - controlling powers. And Neville Longbottom could also be involved, perhaps using his new - found confidence to support Harry in his reality - altering adventures.
Ron would be there too. He could be in charge of things like the Gryffindor common room or helping Harry with student relations. And of course, Dumbledore might still have some influence in the background, even if Harry is in control. His wisdom could be a guiding force for Harry as he navigates running the school.
The main characters would start with Harry Potter. Then, there could be some members of the pure - blood families. For instance, Draco Malfoy could be a key character. His family's obsession with blood purity and his own complex relationship with Harry could be further explored in the context of Harry's control over blood magic. Also, characters like Neville Longbottom could be involved, perhaps his connection to his family's history through blood could be related to Harry's new power.
The main character is most likely Harry Potter as he is the focus of the transformation into a metal dragon. However, depending on the direction of the fanfiction, there could be new characters introduced. For example, a wizard or witch who has knowledge about metal - based magic or dragons could play a significant role. But the core characters from the Potter series, such as Dumbledore or Snape, may also be involved in different ways, perhaps trying to guide Harry in his new state or dealing with the implications of his transformation on the wizarding world.
It could be Orochimaru. He's always been interested in new and powerful jutsus. He might see Naruto's shadow - controlling ability as something he wants to steal or use for his own evil purposes.
It could be a rogue Huntsman who wants to use Ruby's power to control Grimm for his own evil purposes. He might believe that with the Grimm under his control, he can rule over Remnant. He would then be constantly trying to kidnap Ruby or figure out the secret behind her power, and would oppose team RWBY at every turn.