Who could be the main antagonists in a 'Percy Jackson Champion of Hecate Fanfic'?

Some of the more powerful and vengeful spirits in the Underworld itself could be antagonists. They might not want an outsider like Percy to be the Champion of Hades. They could try to undermine him at every turn, like spreading false rumors about him among the other Underworld denizens or directly attacking him when he's vulnerable during his quests in the Underworld.

The Titans could be antagonists. They might see Percy as a threat since he's Nyx's champion. They could try to stop him from fulfilling Nyx's tasks or even try to turn him against Nyx.

A powerful sorcerer who once was a disciple of Hecate but turned to the dark side could be the main antagonist. He might be jealous of Percy being chosen as the champion and wants to steal Percy's powers for himself.

The Titans could still be antagonists. Since Percy has a connection to Hecate, they might see him as a threat to their plans of overthrowing the gods. They could try to capture him to use his powers for their own evil purposes.

The children of Ares might also act as antagonists. They are often at odds with the followers of Aphrodite in the Percy Jackson universe. They might see Percy being the champion of Aphrodite as a threat to their own power and influence. So, they could constantly try to pick fights with Percy, both physically and by trying to turn other demigods against him.

Perhaps some rogue demigods who have turned against the gods and don't believe in Hestia's values. They could be jealous of Percy being chosen as her champion. They might try to undermine his efforts and steal any power or artifacts related to Hestia that Percy is protecting. They could form a sort of anti - Hestia group, causing trouble for Percy at every turn.

One main antagonist could be Nyx, the goddess of the night. Since Apollo represents the sun, Nyx might see Percy as a threat as he is the champion of Apollo. She could try to plunge the world into eternal darkness and send her monstrous children to stop Percy.

Maybe some rogue demigods who are power - hungry. They see Percy's new title as Champion of Ouranos as a way to gain ultimate power. So they would try to either take the title from him or prevent him from using his powers. They could form a secret group and plot against Percy, using their own demigod abilities and knowledge of the demigod world to their advantage.

The obvious antagonists could be the monsters that are constantly trying to thwart Percy's plans. For instance, the Minotaur could make a comeback, being more powerful and cunning this time. It might be under the control of a more powerful force that doesn't want Percy to succeed as Hera's champion.

The Furies could also be major antagonists. They are already powerful and feared in the Underworld, and Percy as the Champion of Erebus might be seen as a threat to their authority. They could try to undermine him at every turn, setting up traps and sending various minions after him. Additionally, there could be a new, unknown force emerging from the darkest parts of Erebus that is opposed to Percy's role. This could be a primordial being that has been awakened by Percy's ascension and wants to return the Underworld to a more chaotic and lawless state.