Who could be the main antagonist in a 'Percy Jackson Guardian of Artemis fanfiction'?

A possible main antagonist could be a rogue demigod who was once rejected by the Hunt and now wants revenge. This demigod could have allied with some powerful monsters and is constantly causing trouble for the Hunt. For example, they might be stealing important artifacts or sabotaging the Hunt's missions.

A powerful Titan who was banished to the moon in the past and now wants revenge on the gods by destroying the moon could be the main antagonist.

It could be a powerful demigod who has been corrupted by greed. He wants to use the power of the earth for his own gain, like creating his own kingdom or something. So he's trying to stop Percy from protecting the earth because Percy stands in his way.

It could be an ancient and vengeful Titan who was once imprisoned by the Hunters' predecessors. Now free, it wants to destroy the Hunters to regain its lost power and take revenge on those who once locked it away.

A powerful Titan who has a grudge against both Percy and the Hunters of Artemis could be a great antagonist. Maybe he wants to use the power of the Hunters for his own evil purposes or destroy Percy to get revenge on the gods.

There could also be a group of rogue demigods who oppose the daughter of Artemis. They might be jealous of her powers or her connection to Artemis. They could try to sabotage her and Percy's quests and cause trouble for them at every turn.

It could be a rogue demigod who wants the throwing stars for their power. This demigod might have been shunned by the other demigods and sees the stars as a way to gain revenge and power over them.

It could be a new demigod who has turned to the dark side. Jealous of Percy's popularity and Artemis' power, this demigod could try to create chaos in the high school and turn students against them.

A good antagonist could be a powerful and vengeful centaur. Centaurs are known for their knowledge and combat skills. This centaur could have a grudge against both Percy, perhaps because he defeated some of the centaur's friends in the past, and the Hunters of Artemis because they protect the forests that the centaur wants to claim for his own evil purposes.

A powerful and corrupted nymph could be the main antagonist. She was once a friend to the Hunt but was lured to the dark side by some ancient magic. Now she wants to destroy the Hunt and take over their territory. She uses her powers over nature to create all sorts of obstacles for the Hunt and Percy, if he's involved. She could also be very manipulative, turning some of the Hunt members against each other.