Who could be Percy Jackson's main antagonist in a 'Percy Jackson Champion of the Arena' fanfiction?

It could be an old enemy of Percy who has somehow gained power over the Styx. Maybe a resurrected villain from Percy's past who now wants to use the power of the Styx to take revenge on Percy and the gods. For example, Kronos' remnants could have found a way to manipulate the Styx's energy for their own evil purposes.

A powerful Titan who has somehow escaped Tartarus and is bent on revenge against the gods could be a great antagonist. This Titan might see Percy as a key figure in the new order of the gods and fates, and so wants to destroy him. Maybe it's someone like Atlas, who has a long - standing grudge against the Olympians and now wants to take it out on Percy as the champion of the fates.

There could be a new Titan that we haven't seen before. This Titan could be more cunning and powerful than the others. Maybe he's been in hiding all this time, waiting for the right moment to emerge and lead the Titans to victory. He could manipulate Percy's friends against him and create all sorts of problems for our hero.

Another antagonist could be a powerful frost giant. If Percy is involved in protecting Asgardian interests related to Thor, a frost giant could be a major foe. They are strong and have their own motives for opposing Thor and his champion. They might see Percy as an easy target at first but soon realize his strength.

It could be one of Mars' old enemies, like a powerful Titan who has a grudge against Mars and sees Percy as a threat. Maybe this Titan wants to take over Mars and Percy stands in the way.

Perhaps a powerful sorceress from an ancient line that has a long - standing grudge against the demigods. She sees the sister as an easy target at first, but as the story progresses, she realizes that the sister is much stronger and more determined than she thought. So she becomes more and more desperate to defeat her and stop her from fulfilling her destiny.

It might be a mortal who has been given special powers by the gods for a specific purpose. This mortal could be an unlikely hero, but through a series of events, they are chosen to be the 'Champion of the Sun'. They would then have to learn to control their new - found sun - related abilities and face the challenges that come with the title.

A powerful demigod who has been corrupted by the idea of primordial power could be the main antagonist. They might believe that by allying with a primordial or obtaining their power, they can become greater than the gods. This demigod would then oppose Percy, who stands for the protection of the current order.

An ancient and forgotten god who has been awakened. This god could be angry at the modern demigods for ignoring the old ways and decides to send assassins after Percy as a warning to the rest. They might want to bring back the old order where gods were feared and worshiped more and see Percy as a symbol of the new, more independent demigods.

Perhaps an ancient and dark deity who has been awakened due to some event related to Percy's exile. This deity wants to bring chaos to the world of gods and demigods, and Percy, even in exile, is the only one who can stop it. The deity would use all kinds of dark magic and minions to oppose Percy and his friends.