Who could be the main antagonist in 'harry is a shapeshifter fanfiction'?

Maybe there could be a new antagonist, a dark shapeshifter who is jealous of Harry's power. This antagonist could be an old wizard who has been in hiding for centuries, waiting for the right time to emerge and take over the wizarding world. He sees Harry as a threat to his plans and tries to eliminate him.

Perhaps a group of rogue ninjas who are threatened by Naruto's shapeshifting ability. They might see him as a threat to their plans and try to eliminate him. They could be led by a mastermind who is well - versed in countering shapeshifting techniques.

A long - lost relative of Sirius Black could be a shapeshifter. Since the Blacks had many secrets and were involved in a lot of dark magic in their family history, it would be believable for a hidden relative to have this unique ability.

A power - hungry merman who wants to rule over all the mer - people. He sees Harry as a threat because Harry has some special powers or a claim to the throne that he doesn't want to share.

A new dark wizard who has emerged from the shadows, someone who idolized Voldemort and is trying to pick up where he left off. This antagonist could be using new and more insidious magic that Harry has to figure out how to combat as an Auror.

A power - hungry noble could be the main antagonist. This person might be jealous of the Queen's position and wants to overthrow her, and sees Harry as an obstacle in his way.

It could be a villain from Harry's world who is jealous of his new connection with the Starks. Maybe a dark wizard who wants to steal Stark technology to enhance their own dark magic.

It could be a corrupt prison warden who has a personal vendetta against Harry. This warden might make Harry's life in prison extremely difficult and try to prevent him from ever getting out, even if he's innocent.

There could be an ancient force that is awakened by the meeting of Harry and Hela. This force wants to destroy both of them because their combined powers could potentially stop it from achieving its goal of spreading chaos and destruction throughout all the realms. It would use all kinds of devious means to try and separate them and defeat them one by one.

A new dark wizard or witch could be created specifically for this fanfiction. This character could be interested in using the Huntsman's skills for their own evil purposes. If the Huntsman refuses, they become enemies. This antagonist could have powers related to dark forest magic, something that the Huntsman is familiar with but in a more malevolent form.