One idea could be a prequel focusing on the characters' lives before boarding the Poseidon. For example, showing how they got their tickets and what led them to be on that fateful journey.
A plot could involve a group of survivors from the initial disaster in 'The Poseidon Adventure' who are then faced with new challenges while trying to escape the still - sinking ship. Maybe they discover a hidden part of the ship that holds secrets or valuable resources that can help them survive.
Well, you could base your fan fiction on a 'what if' scenario. What if the adventure in 'Adventure of a Lifetime' took place in a post - apocalyptic world instead? The characters would have to face new challenges like mutated creatures and scarce resources. Or perhaps you could write a fan fic where the adventure is a dream within a dream. The main character thinks they've completed one adventure, but then wakes up to find they're still in another adventure that's even more dangerous and mysterious. You might also consider making the adventure a race against time to save a dying world, with the characters having to overcome not just physical obstacles but also moral dilemmas.
One plot idea could be that the OC is a young mermaid who accidentally crosses into Poseidon's territory. Poseidon, initially angry, is intrigued by her courage. Another could be the OC is a mortal with a special power to control water to a small extent, and Poseidon takes an interest in mentoring the OC. Or perhaps the OC is a demigod sent on a quest by the gods, and Poseidon has to decide whether to help or hinder the OC.
One plot idea could be Percy having to go on a quest specifically guided by Poseidon's hidden messages in the sea currents. He has to decipher these messages to find a lost artifact that can save the underwater kingdom from a new, mysterious threat.
One idea could be Percy having to face a new threat underwater that only Poseidon can help him understand. Maybe a lost civilization that Poseidon once had a connection with is now causing trouble. Another could be Percy going on a quest to find a powerful artifact that was once Poseidon's but has been stolen, and Poseidon gives him special powers or guidance along the way.
Perhaps there's a story where Poseidon falls in love with Gabrielle. Xena has to protect her friend from the powerful god's advances while also trying to keep the balance in their world. This could lead to a lot of drama and action as they navigate the complex situation.
One plot idea could be a story where Poseidon and Athena have to team up to face a common threat to the pantheon. Maybe a new and powerful deity emerges who wants to overthrow the existing order. Their different powers and personalities would create interesting dynamics as they try to work together.
In this type of fanfiction, a possible plot is that Poseidon raises Percy away from Camp Half - Blood to protect him from the prophecy. As Percy grows up, he becomes more in tune with his water powers. He could then have adventures in the ocean, like finding lost civilizations or facing off against sea monsters that Poseidon sends his way to test him.
In a fanfiction, Poseidon and Zeus could be involved in a bet. The bet could be about who can better handle the affairs of a particular mortal city for a certain period. As they interfere in the mortal world, they learn more about each other's capabilities and develop a newfound respect.
Definitely the main protagonist from the original story. Their courage and leadership can be further explored in fan fiction. For example, how they make split - second decisions in even more dangerous situations.
One idea could be a story where the Mandalorian has to team up with an old enemy to fight a new, greater threat. Maybe a powerful Sith Lord emerges and they have to put aside their differences.