Who could be the main antagonist in a 'Jason meets Percy Jackson fanfiction'?

There could be a new, made - up character. A digital wizard of sorts who has learned how to cross over from the popularmmos world to the Percy Jackson world. He wants to control all magic and technology, believing that by merging the two worlds under his rule, he can become the most powerful being. So he sets out to stop anyone who stands in his way, including Percy and the popularmmos crew.

A group of rogue demigods could be the antagonists. They are jealous of Percy and Jason's fame and power. They form a secret alliance and start causing trouble for the other demigods. Percy and Jason meet while trying to figure out who is behind these attacks. At first, they suspect each other, but then they realize the real culprits are this group of rogue demigods and join forces to stop them.

It could be an ancient sea creature that was once imprisoned by Amphitrite and Poseidon. Now that Percy has come into the picture, it senses an opportunity to break free. It uses its dark powers to manipulate the ocean and turn it against Percy and Amphitrite, hoping to create enough chaos to shatter the chains that bind it once again.

Well, they could start off on the wrong foot. Maybe Jason is a bit too by - the - book Roman and Percy is his carefree Greek self. But then they'd realize they have a lot in common, like their heroic natures. They might team up to fight a common enemy, using their unique powers. Jason with his lightning and leadership skills, and Percy with his water - based powers and street - smart thinking.

It could be a new monster that is specifically targeting Percy's mortal connections, like Paul. Maybe a monster that feeds on the fear of mortals who are close to demigods.

Maybe a group of mercenaries who are also interested in the valuable artifacts related to Greek mythology. They would be willing to do anything to get their hands on them, and they are a threat not only because of their weapons but also because they have some knowledge of the ancient secrets that could be used against Percy and Lara. They could set up ambushes and try to steal the artifacts from Percy and Lara while they are in the middle of their exploration.

It could be a power - hungry Atlantean noble who wants to rule not just Atlantis but also the surface world. He sees Percy as a threat to his plans and tries to stop him at every turn.

A new and powerful demon that has emerged from the darkest corners of the underworld. This demon is bent on using Percy's connection to the overworld to break through the barriers between the two worlds and unleash chaos. It has powers that are different from what Percy has faced before, like the ability to manipulate the very essence of the underworld's environment.

A powerful Amazonian sorceress who has turned against her own kind and is now trying to use dark magic to take over the world. She could see Percy as an obstacle in her path and constantly try to defeat him.

Maybe it could be a demigod who has become obsessed with power through gaming. This demigod, let's say a child of Hades, discovers a way to use dark magic and combine it with gaming technology to try and rule over all the other demigods. He sees Percy as a major threat to his plans because Percy is so popular and has strong powers, so he constantly tries to undermine Percy at every turn.