It could be a group of mythical creatures that have been experimented on by Shield. They've become more powerful and angry, and they see Percy as a threat. They target him and try to destroy him, as well as causing chaos within Shield. These creatures could be something like mutated centaurs or enhanced harpies.
Maybe there's a high - ranking official within Shield who has his own agenda. He wants to use Percy's powers for his own gain, and when Percy refuses, he becomes the main antagonist. He has access to all of Shield's resources and uses them to try and capture Percy, setting up traps and sending out teams of agents to hunt him down.
Luke could be a great choice. He already had his moments of turning against the good side in the original series. He could be resurrected or something and become an assassin with a powerful shield, using his combat skills and knowledge of the demigod world to his advantage.
A likely main antagonist could be a powerful demigod who has turned to the dark side and wants to use chaos for his own evil purposes. He might see Percy as a threat to his plans.
Well, it could be about Percy using his demigod powers in the world of Shield. Maybe he's on a mission to uncover a conspiracy within Shield that threatens the demigod world. He could use his water - controlling abilities to his advantage, like creating distractions during battles or escaping tricky situations.
The Giants might also be antagonists. They could band together and target Percy's kingdom, believing that by destroying him and his rule, they can undermine the power of the gods further. They might use their brute strength and strategic thinking to attack Percy from different fronts.
Another option could be a group of rogue demigods who have turned to the dark side. They follow Percy to Forks, hoping to find some powerful artifacts there. They don't care about the vampires or werewolves and are willing to cause destruction to get what they want. Percy has to stop them while also dealing with the local supernatural creatures.
Maybe the gods or powerful beings who are trying to maintain the current balance and see Percy's new role as a disruption. They would try to stop him from carrying out his assassinations in the chaos world.
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.
Well, in the 'Percy Jackson hunted by Shield' fanfiction, Percy's main source of help would be his demigod comrades. Annabeth Chase, with her brilliant mind and knowledge of architecture and strategy, could help Percy plan his escapes and defenses. Grover Underwood, being a satyr, has a connection with nature that could be used to create barriers or mislead Shield's agents. Additionally, Chiron, the centaur trainer at Camp Half - Blood, might have some ancient knowledge or magic that could be used to protect Percy or make him less detectable to Shield. There could also be other demigods with unique powers that could come to Percy's aid, for example, those with the power of invisibility or mind - control who could use their abilities to disrupt Shield's operations.
Well, the main antagonists could be a group of rogue demigods who have formed a cult around Kronos. They believe that Percy, as the heir of Kronos, should lead them in overthrowing the current order of the demigod world. But Percy doesn't want any part of it, so they become his enemies. Another possible antagonist could be an ancient being that was once in league with Kronos and now sees Percy as a means to resurrect Kronos or continue his dark legacy. This being would stop at nothing to force Percy to embrace his role as the heir.
Perhaps some of the older, more traditional gods could be antagonists. They might see Percy as a threat because he's now the God of Dinosaurs and they fear the power he could gain from controlling these ancient and powerful creatures. For example, Zeus might be worried that Percy's new role could disrupt the existing power balance among the gods.