Perhaps a jealous wizard from an old family who sees Harry's new inheritance as a threat to their own status in the wizarding world. They might try to undermine Harry at every turn, spreading false rumors about him or trying to sabotage his attempts to understand and use his inheritance.
There's a possibility that an ancient magical entity that has been dormant for a long time is awakened by Harry's inheritance. This entity might see Harry as a tool or a threat and thus becomes the main antagonist. It could use its dark magic to try and control Harry or prevent him from fully realizing his inheritance. The entity might have its own motives related to the past history of the wizarding world and Harry's newfound connection through the inheritance test.
It could be a dark wizard who wants to steal Harry's inheritance for his own gain.
In this kind of fanfiction, Harry might discover some unexpected magical inheritances. For example, he could inherit a powerful ancient magic or a special magical artifact from a long - lost relative. This new inheritance could change his status in the wizarding world and also give him new powers to fight against Voldemort or other dark forces.
Maybe a dark wizard who has an interest in Harry's newfound inheritance. This antagonist could want to steal his powers or use him for their own evil purposes. They might see Harry as a key to unlocking some ancient and powerful magic that they've been seeking.
The main antagonist could be a Slytherin student who has a vendetta against Harry. When they see Harry with the snake, which they believe should belong to a Slytherin, they start causing trouble for Harry. They might try to frame Harry for using dark magic with the snake or try to steal the snake to prove their superiority over Harry.
It's hard to say for sure without reading it, but likely Harry Potter himself would be a main character. He's the central figure in the original series, so it would make sense for him to be involved in an inheritance test. Hermione Granger could also be a main character as she's always been very involved in the magical mysteries.
Well, in such a fanfiction, Harry might discover some hidden magical powers or a special bloodline connection. It could lead to him having new allies or facing new enemies who are interested in his newfound inheritance.
Voldemort could still be the main antagonist. His dark magic would be in direct contrast to Harry's angel inheritance. He would see Harry as an even greater threat now and would do everything to stop Harry from fully realizing his new powers.
Dumbledore could play a crucial role. As the wise headmaster, he may have some prior knowledge about Harry's possible inheritances. He could guide Harry through the process, explaining the significance of any new powers or items he has inherited and how to use them for the greater good of the wizarding world.
It could be a jealous Slytherin student. Since snakes are often associated with Slytherin, this student might feel that Harry has no right to take care of a snake. They could try to steal the snake or cause trouble for Harry, like spreading rumors that the snake is dangerous and should be removed from Hogwarts.
Maybe it's a dark wizard who has an interest in the snakes Harry is taking care of. He wants to use the snakes for some dark magic purposes. So he constantly tries to steal the snakes from Harry or even harm Harry to get to the snakes. For example, he could be a follower of Voldemort who believes the snakes hold some special power that can help bring back the dark lord.
It's hard to say without reading it, but it could be the main trio - Harry, Hermione, and Ron. They often get involved in all kinds of magical situations in fanfiction.