There could be an old wizard who was once shunned by the Potter family. In revenge, he casts a spell on Harry that makes him think his name is 'freak'. This wizard could be lurking in an abandoned part of the wizarding world, waiting for the right moment to strike again or to see Harry completely lose his sense of self.
In a 'harry thinks his name is freak' fanfic, it could start with Harry being in a new magical environment, like a hidden part of the wizarding world. Here, everyone refers to him as 'freak' for some reason he can't understand at first. It could be a cultural difference or a misinterpretation of his powers. As he tries to adapt to this new identity, he discovers secrets about this part of the wizarding world that are related to his real name and his true place in the magical community.
It could be an archaeologist who has been corrupted by the power of an ancient artifact related to the mummy. This archaeologist wants to use the mummy's power for his own gain, like becoming immortal or ruling the world. He would be constantly trying to stop Harry from helping the mummy.
It could be a powerful dark wizard who has also gained some supervillain - like powers. This antagonist might be jealous of Harry's newfound superhero status and wants to destroy him.
It could be a jealous wizard who feels that Harry and his sister are getting too much attention in the wizarding world. This wizard might try to undermine their achievements and even put them in danger.
The main antagonist could be a powerful necromancer who combines the dark arts of Skyrim with some elements of Voldemort - like magic. He could be raising an army of the undead and causing chaos across Skyrim, which Harry has to stop.
It could be Voldemort or one of his Death Eaters. They might be using Harry as a pawn to get to Parvati for some reason, like she has a special power or knowledge that they want.
Maybe an ancient evil spirit that was once bound but is now trying to break free by using the summoner as a conduit. This spirit could be manipulating events from the shadows, causing chaos in the wizarding world to draw the summoner out.
There could be a group of purist wizards who believe that magical animals should not be put on display for non - wizards to see. They constantly try to disrupt the zoo's operations, causing trouble for Harry. Harry would need to fight for the right of his zoo to exist and educate these purist wizards about the importance of co - existence between wizards, non - wizards, and magical animals.
It could be a rogue wizard who has infiltrated SHIELD and is using their technology for dark magic purposes. This wizard might be jealous of Harry's new position and try to undermine him.
It could also be an old and powerful magical creature that has been awakened by some dark magic. This creature sees Harry as a threat to its existence because of his mastery of magic and decides to target him. For instance, a dragon that has been enchanted with dark magic to be more intelligent and malicious.