A great plot for Shadow the Hedgehog game fanfiction could involve Shadow's relationship with other characters. For instance, a story about how he forms an unlikely friendship with a young and naive creature in the Sonic world. He then has to protect this new friend from the chaos and danger that constantly lurks in their world. This would show a different side of Shadow, his more protective and caring side.
One idea could be that Shadow discovers he has vampire-like abilities after a strange encounter in a dark, enchanted forest. He then has to struggle with his new thirst for blood while still trying to protect his friends and the world from villains.
One plot idea could be that Shadow and Amy are on a mission together to save Sonic who has been captured by a new villain. Along the way, they start to understand each other's motives and personalities better. Amy's positive attitude might start to rub off on Shadow, who is usually more brooding.
One idea could be that Shadow somehow gets transported into the Harry Potter world. He might use his speed and combat skills to help the students at Hogwarts during a time of great danger, like when Voldemort's forces are attacking. Maybe he teams up with Harry and they learn from each other's fighting styles.
One idea could be that as a girl, Shadow has to face different challenges in a male - dominated Sonic world. Maybe she has to prove herself constantly to be accepted as a strong fighter.
One idea could be Sonic having to deal with his new vampire abilities while still trying to protect his friends from the usual villains. For example, he might struggle with the urge to drink blood but not want to harm his friends. Another plot could involve Sonic trying to find a cure for his vampirism while on the run from vampire hunters who mistake him for an evil creature.
A really interesting plot for 'Game of Thrones and Shadow of War fanfiction' would be if the Nemesis system from 'Shadow of War' was applied to 'Game of Thrones'. Imagine if every time a character in 'Game of Thrones' wronged another, that wronged character became stronger and more vengeful like the orc captains in 'Shadow of War'. So, for instance, if Cersei wrongs Tyrion too much, Tyrion could become a super - intelligent and powerful 'Nemesis' figure, plotting his revenge in a much more complex and dangerous way than in the original series. This would add a whole new layer of drama and power - play to the 'Game of Thrones' world.
One idea could be that Shadow somehow gets transported to the My Little Pony world. He might initially be a bit of an outcast due to his different and edgier personality compared to the ponies. But as the story progresses, he could learn about friendship and harmony from them and in turn, teach them about his own values like loyalty and justice in a different sense.
One possible plot could be that Shadow and Twilight are brought together by some sort of interdimensional rift. They then have to work together to find a way to close the rift and in the process, they learn about each other's worlds and powers.
One idea could be Silver coming from the future to prevent a new threat in the Sonic X universe that the others are unaware of. He might team up with Sonic and his friends in unexpected ways, like using his psychic powers to help them access hidden areas. For example, he could use his powers to levitate Sonic over a large chasm that the others can't cross.
One idea could be Sonic having to face a new and more powerful dark version of the Black Knight. This would test his skills and force him to find new ways to use his speed.