One idea could be exploring the backstory of War before the events of the first game. Maybe show his training and early battles that shaped him into the Horseman we know.
You could write a fan fiction about the relationship between Death and War. How they interact when not on a mission, and their different views on the balance of the universe.
Another interesting idea is to create an alternate universe where the Horsemen are not the bringers of the apocalypse but rather protectors of a different kind of order. This could lead to new adventures and interactions with the existing characters.
Another plot could involve a crossover within the Darksiders universe. Maybe the Horsemen have to team up with a previously unknown group of characters to face a new, greater threat. This could introduce new dynamics and relationships.
One idea could be a crossover where the characters from Naruto end up in the Darksiders universe and have to fight the demons there using their ninja skills. For example, Naruto could use his shadow clones to confuse the hordes of demons while Sasuke uses his Sharingan to predict their moves.
One idea could be creating an OC who is a hybrid of different races in the Darksiders universe. For example, a half - angel, half - demon character. This would bring a unique perspective as they struggle with their dual nature, being neither fully accepted by the angels nor the demons.
Perhaps the Avengers mistake one of the Horsemen for a new super - villain. As they engage in battle, they soon realize that the Horsemen is actually after a powerful artifact that a real villain in the Avengers' world has obtained. So they form an uneasy alliance to retrieve the artifact.
Another interesting concept for a Darksiders War crossover fanfiction could be a crossover with the Diablo series. Imagine the dark and gritty world of Diablo mixing with the post - apocalyptic world of Darksiders. The heroes from Darksiders could be lured into the world of Sanctuary in Diablo, where they have to deal with the hordes of demons while also trying to find a way back home.
One idea could be that the Horsemen from DarkSiders end up in the world of RWBY. Maybe War arrives first and is mistaken for a powerful Grimm. He then has to figure out how to interact with the Huntsmen and Huntresses while also trying to find a way back to his own realm. Another idea is that the characters from RWBY somehow stumble into the post - apocalyptic world of DarkSiders and have to adapt to the harsher and more dangerous environment.
Another possibility is a crossover with 'God of War'. Death and Kratos could meet. Given their both powerful and somewhat vengeful natures, they could either become bitter enemies or reluctant allies. The story could explore their different views on death, with Death being an embodiment of it and Kratos having a very personal and violent relationship with death in his own journey.
One plot idea could be Uriel embarking on a quest to find a lost relic in the Darksiders universe. Along the way, she encounters various challenges and forms an unexpected alliance with a character who has a mysterious past. This could lead to a lot of character development and exploration of the Darksiders world.
Well, you could write a fan fic where the relationships between the characters are reversed. So if in the original there are certain rivalries, in the fan fic they become allies and vice versa. Also, a story about a character who loses their power but discovers a new way to be strong within the 'unordinary' world would be interesting. Or how about a fan fic that takes place in a parallel dimension within the 'unordinary' universe where the rules of powers are slightly different?
Some interesting ideas for Riverdale fan fiction could be a crossover with another popular teen drama. Imagine the characters of Riverdale meeting the characters from 'Stranger Things'. It would be really cool to see how they interact. You could also write a fan fiction that focuses on the future of Riverdale. What will happen to the town and its residents ten years from now? Will Archie still be in town? How will Veronica's business empire develop?