(this is a response to the game thing) Yes, i will include all of the primal versions of pokemon, heres a qiuck part of the story.
In the battle, Arceus uses a move called Darkness falls (also the name of the card thing im making, look at sig) It turns all pokemon with a dark side, dark. But, the ones who dont have a dark side all form a circle around them and all of them yell there names, causing them to turn normal, then all the pokemon hold each others...hands or wings, or something and they all yell there names, then they all go to what looks like a hero form (NEW!) and they al use there main moves (for example, dialga: Roar of time, etc...) and the battle will continue on. (btw there is an epic thing that Arceus does, its when they all do there most powerfulest move, it makes a big explosion, and arecus comes out of the smoke with very few bruses. EPIC!)
Theres a little bit you will know of. And the overworld sprites will be from mystery dungeon.