One way their worlds could collide is through the concept of magic. In the Percy Jackson universe, there's Greek magic, and Doctor Strange is a master of the mystic arts. Maybe Percy could end up in the Sanctum Sanctorum by accident and Strange has to figure out how to send him back to his world. It would be a wild adventure as Percy's demigod powers might react strangely to the magic in Strange's world.
Well, the characters could meet if there was a threat that spanned both their universes. For example, a powerful being that feeds on both magic and the power of the Greek gods. Percy and his friends would team up with Doctor Strange and his allies. Percy's sword fighting skills combined with Strange's spellcasting could make for some epic battle scenes against this new threat.
The worlds could collide through a portal. Maybe a demigod accidentally creates a portal while trying out a new spell. This portal leads to the world of the Transformers. Percy Jackson and his friends are then sucked into this new world. They find themselves in the middle of the war between Autobots and Decepticons and have to choose a side or find a way to create peace between the two factions.
Well, in a fanfiction scenario, the immortal Percy Jackson could bring his demigod powers to the Avengers' world. Maybe his water - controlling abilities could help in battles against villains who use fire - based attacks. For example, against a foe like Ultron, Percy could douse his mechanical parts and disrupt his systems.
The technology in Steve's world and the magic in Percy's world would be a huge point of contrast. Steve has advanced weapons and technology at his disposal, like his shield. Percy has his Riptide sword and his powers. When these two elements meet, it could lead to some really creative solutions. For instance, they could use Percy's water powers to power up some of Steve's tech that needs an energy source. Or Steve's tech could be used to track down a mythological creature that's hiding in a modern city.
Well, one way their worlds could collide is through a common enemy. Maybe some ancient Greek monster has found a way into the modern world of the Avengers. Percy, with his water - controlling powers and combat skills, could team up with Thor, who also has power over a natural element. They would make a formidable duo against this threat.
One way the worlds could collide is through a magical accident. Maybe some of the Infinity Stones' power messes with the magic in Percy Jackson's world, causing portals to open. Percy and his friends could be sucked into the Avengers' universe right in the middle of the Civil War. They might side with different factions based on their own beliefs about power and control.
Their worlds could collide when a mythological creature shows up in a Shield - protected area. This would force Shield agents to deal with something beyond their normal scope, and Percy would be called in to handle it because of his knowledge of the mythological world.
A possible fanfiction could involve a crossover where some of the Avengers are sent to Camp Half - Blood. Imagine Tony Stark trying to figure out how the magic at the camp works while also being highly amused by the whole concept of demigods. Steve Rogers could bond with some of the more heroic demigods over their shared sense of duty. Meanwhile, Percy and his friends have to keep an eye on the Avengers to make sure they don't accidentally disrupt the delicate balance of the camp. And then, they all have to face a threat that targets both the Avengers and the demigods, like a group of villains who want to steal the powers of both.
Perhaps there's a plot where the dinosaurs are being used by an evil force. The evil force has found a way to control the dinosaurs and is using them to attack the demigod camps. Percy and his friends then have to figure out how to break the control and save the day. They might find out that the dinosaurs have a connection to an old Greek god or goddess that they didn't know about before.
One idea could be that Percy finds himself magically transported to Skyrim. He could use his water - based powers in the frozen landscapes, like creating ice bridges over rivers or using water currents to his advantage in battles against the various creatures in Skyrim.
One idea could be that Percy Jackson discovers a hidden Cybertronian relic. This relic has the power to control water in a way that even Poseidon's trident can't. The Autobots and Decepticons are both after it. Percy has to team up with the Autobots to keep it out of the Decepticons' hands and also figure out how it relates to his world of Greek gods.