Yu-Gi-Oh! Crossover Challenge
The challenge is this: A character, you can decide which one, lands in the world of the Duel Monsters cards. Think Yu-Gi-Oh! OCG Stories. For example, they could land in the Forest and run afoul of the Black Garden and/or the Traptrix. They could get captured by the Amazoness monsters and have to fight for survival in Amazoness Arena. They could stumble upon the Sky Striker war between Raye and Roze. They could land in Necrovalley and contend with the Gravekeepers and other Egyptian themed cards. They could participate in the battle between the good and evil Kozmo cards. They could deal with the Archfiends and Dark World monsters. The possibilities are endless.
You know what? One day, I would like to do this story with Kuzuno Sekai from the manga Time Stop Brave as the protagonist, but it would likely be rated M.