One idea could be Percy having to face Medusa in a new way that challenges his usual methods. Maybe he gets trapped in a dream where Medusa has the upper hand and he has to use his wits more than his sword. Another could be a scenario where Medusa is somehow redeemed and teams up with Percy against a greater evil. For example, an ancient monster that threatens both the mortal and mythological worlds.
In a 'Percy Jackson x Medusa fanfiction', there could be a plot where Medusa's lair is discovered to be a gateway to a different dimension. Percy has to work with Medusa, who is the guardian of this gateway, to close it before a horde of demons from the other side invade. Their relationship starts off as hostile, but as they face challenges together, they begin to understand each other better. Percy realizes that Medusa wasn't always the heartless monster she seems, and Medusa sees that Percy is different from other demigods who have tried to kill her.
One idea could be Percy has to face Medusa again, but this time she has an army of stone minions. Another could be that Medusa was actually cursed by a more powerful god and Percy has to find a way to break it. Maybe Percy discovers Medusa has a long - lost relative who is being held hostage and he has to make a deal with her.
One idea could be that Percy has to face a new threat from Medusa's long - lost sister who has even more powerful petrifying abilities. He has to use his skills and some newfound knowledge about the Gorgon lineage to defeat her.
One idea could be Percy using his water powers in a unique way against Medusa. For example, he could create a water shield that reflects Medusa's petrifying gaze back at her in a fanfiction. Another could be a scenario where Medusa, instead of being an enemy, teams up with Percy to face a greater threat.
In a fanfic, perhaps Percy and his friends accidentally stumble upon Medusa's lair while on a quest. But instead of immediately attacking, Medusa offers them a deal. She says she will give them a valuable clue to complete their quest if they help her get revenge on one of the minor gods who wronged her in the past. Percy and his friends then have to decide whether to trust Medusa or not.
One idea could be a story where Sally has a premonition about Percy's next big adventure and tries to secretly prepare him for it. Another could be a story set in an alternate universe where Sally has demigod powers herself and she teams up with Percy on a quest. Maybe a story where Sally gets transported into Percy's world at Camp Half - Blood and has to navigate the strange new environment while Percy protects her.
One idea could be Percy exploring an underwater realm that only Poseidon can access. He discovers ancient secrets about his father's past and the origin of his powers. Another could be a story where Percy has to team up with Poseidon to fight a new and powerful sea - born enemy. Maybe there's a prophecy that only their combined strength can fulfill.
One possible storyline could be Percy having to face Medusa in a new way that doesn't involve just slaying her. Maybe he discovers that Medusa has a side to her that was misunderstood all along. For example, she was cursed not out of pure evil but due to the jealousy of the gods. Percy could then try to find a way to break her curse, leading to an unlikely alliance between them.
One idea could be a time - travel plot where Percy goes back in time and meets a younger, different Medusa before she was turned into a monster. Another could be a story where Medusa somehow gets a chance at redemption and Percy has to decide whether to trust her or not. Maybe a plot where they have to team up to defeat a greater evil that threatens both of them.
Another plot could involve Percy getting a vision from Athena about a future threat to the demigod world. But the vision is so cryptic that he has to work closely with Athena to decipher it. Along the way, they build an unexpected bond, different from his usual relationships with other gods. Maybe Percy starts to see Athena not just as a powerful deity but as a mentor figure, and Athena starts to respect Percy's tenacity more than she expected.
One interesting plot could be Percy having to face off against Medusa's other children in a battle of wits and strength. Maybe they are out to prove themselves as worthy as Percy, who has the fame of being Poseidon's son. Another could be Percy having to deal with the stigma of being 'Son of Medusa' in a world that fears her so much. He might have to constantly prove he's not a monster like his 'mother' is perceived.