It could be a dark wizard who wants to use the living werewolf hide for some dark magic. Maybe he wants to create an army of werewolves under his control.
Another possibility is a group of werewolf hunters. They see the living werewolf hide as a trophy and a way to get more power over werewolves. They would be against Harry because he wants to protect the hide and the werewolves associated with it. Harry has to fight against their prejudice and violence. The hunters might have some old grudges against werewolves and are willing to do anything to get the hide.
Perhaps an ancient evil that has been trapped for a long time and the living werewolf hide is the key to its release. This evil entity then tries to manipulate Harry into freeing it by using the mystery of the werewolf hide. Harry has to figure out the true nature of this entity and stop it before it's too late.
It could be that the living werewolf hide is a sentient being in a way. It can communicate with Harry, but only in a very cryptic manner. Harry then has to decipher these messages to figure out what the hide wants from him. It might lead him on a journey to find an ancient werewolf artifact that could either save or destroy the wizarding world.
It could be a dark wizard who wants to get his hands on the lightsaber for its power. He might see it as a new tool to use in his evil plans, like using it to break into Gringotts or to fight off any who oppose him.
It could be a dark wizard who also has an interest in the snake. Maybe he wants to use the snake's powers for evil purposes, like opening a portal to a dark dimension or controlling other magical creatures. So he becomes the main obstacle for Harry as he tries to protect the snake.
The main antagonist could be an evil werewolf who wants to use Harry's new - found status for his own dark purposes. This werewolf could try to convince Harry to embrace the more savage side of being a werewolf and turn against his friends and the wizarding world. He might also be in league with Voldemort or other dark forces, using Harry as a pawn in a larger, more sinister plan.
It could be a dark wizard who also wants to get to the secrets in the lost library. This wizard might try to stop Harry from exploring the library and getting its knowledge.
A powerful vampire could be the main antagonist. Vampires and werewolves are often enemies in such fictional settings. This vampire could be after Akakuro's pack's territory or have a personal vendetta against Akakuro himself.
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 a new dark wizard who has a vendetta against Harry. This wizard might use a spell to stop Harry from eating, thinking it will weaken him before a final showdown. He could be someone who was once a follower of Voldemort and now wants to take his place and prove himself by getting rid of Harry.
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.
In this fanfiction, the main antagonist could be an ancient evil that has been trapped within the grimoire. Once Harry finds the grimoire, this evil starts to gain power and tries to use Harry to break free completely and spread chaos in the wizarding world.