I would have rewritten the Celebi movie to Celebi bringing Ash and co. to a medeival time, where they find the world embroiled in war. Ash would be a peasent, Misty a warrioress, and Brock a monk (his future). Ash would find his anscestors land is being pillaged and destroyed, so he would have to fight with Misty and Brock in the war against the invaders trying to destroy the time. However, he would learn the hard way not to mess with the past