Dark Giratina, Not really separate layers, but just different files that are eventually combined. It probably could be done with layers, but the way I make digital art I rarely work with layers.
They probably correlated the equations from the game by deriving them from the change of the Pokemon's stats throughout. Or it was given to them by Nintendo directly, I'm not sure.
Dark Giratina, Dude... There's this place where Iive called Jensen Pond... It has a bridge, thats about 10 feet off the water. The water below it, goes down to about 50 or so feet... It's got weeds growing so thick that you can't see... I JUMP INTO IT DDDDDD