Who could be the main villain in a Percy Jackson 3 fanfiction?

Maybe a group of rogue demigods who have decided to take over the Hollow for their own purposes. They could be using the resources of the Hollow in a wrong way, like trying to extract its magic to make themselves more powerful. They would be a formidable foe as they have demigod abilities.

Perhaps a minor god who is jealous of the attention the major gods get. This god decides to cause trouble at the zoo. He could be the one responsible for making the magical creatures in the zoo act up. He would try to stop Percy from uncovering his plans and restoring order at the zoo. He might have some strange powers related to the natural elements found in a zoo, like the ability to make plants grow wildly to entangle Percy or make the water in the ponds turn into quicksand - like substances.

Kronos could make a comeback. Even though he was defeated before, he could find a way to return in a more powerful and vengeful form. He could be the mastermind behind the apocalypse, seeking to finally destroy the gods and take over the world once and for all.

Maybe a new type of monster that is created or awakened during the eclipse. This monster could be immune to most of the demigods' powers during the eclipse, making it a very difficult foe. It could have the ability to manipulate shadows, which are stronger during the eclipse, and use them to its advantage in battles against Percy and his friends.

It could be Kronos again, but in a more powerful and resurrected form. He might have found a way to come back even stronger after his previous defeat and now has a new plan to take over the world of gods and demigods.

Maybe a group of rogue nymphs who are angry at how the demigods have been treating the natural world. They trap Percy as a warning to the other demigods, and he has to negotiate with them and find a way to make amends for the actions of his kind.

A great main villain could be a rogue demigod who has found a way to corrupt the power of the hidden blades. This demigod could be jealous of Percy's fame and power and uses the blades to create chaos among the demigod community. He might be using the blades to steal the powers of other demigods, making him stronger with each theft.

Another option for the main villain is a powerful sorceress who was once a friend of the gods but was betrayed. She has now turned to the dark side and wants to use Percy and his cousins as sacrifices in a dark ritual that would give her unlimited power. She has the ability to create illusions and control minds, which she uses to try and separate Percy and his cousins before she strikes.

It could be a demigod who was once shunned and now wants revenge. This demigod has turned to the dark side and uses their powers in a twisted way to cause chaos among the other demigods. They might target the forgotten demigod specifically because they see them as a symbol of all that is wrong with how demigods are treated.

It could be another Titan who opposes the idea of balance. Maybe a Titan who wants to tip the scales in their favor and create chaos. This Titan could see Percy as a threat to their plans and constantly try to stop him from achieving balance.