Who could be the main antagonist in 'Harry Potter Lost at Sea' fanfiction?

It could be a dark wizard who has also found his way into space. This wizard might be using the new environment to develop even more powerful and dangerous dark magic.

It could be Captain Hook. Since Harry Potter has magic, Hook might see him as a huge threat to his plans in Neverland. He would try to capture Harry and use his magic for his own evil purposes, or simply get rid of him to maintain his control over the island.

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.

Perhaps a magical creature that has made the island its territory. This creature doesn't want outsiders like Harry and his friends interfering. It sees Harry's glasses as a strange and foreign object and will do anything to keep them from leaving the island. It could be a giant spider - like creature that spins webs to trap intruders, just like the acromantulas in the Harry Potter series.

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.

Well, it might be that Harry is lost at sea due to some sort of magical accident. He could meet other magical beings that are native to the sea, such as mermaids. They could either help him or pose a threat. And perhaps he has to find a way to use his Hogwarts - taught magic in new and creative ways to get back to land. He could even discover some long - lost magical artifacts at the bottom of the sea.

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.

Voldemort could still be the main antagonist. Even if Demetri has some sort of connection or change in the fanfiction, Voldemort's overarching evil plans would still be a major threat to both Harry and Demetri, especially if Demetri tries to deviate from the Death Eaters' path.

The minotaur itself could be the main antagonist. It's a powerful and dangerous creature, and if it's been set loose in Hogwarts or is guarding something that Harry needs, it would be a major obstacle for him to overcome.

The main antagonist could be a dark wizard who has made the graveyard his lair. He uses the dark energy from the tombstones and the restless spirits there to power his dark magic. Harry stumbles upon this wizard's activities and has to stop him.