>>14383162Arceus creates everything, including the set pieces for all Pokemon to eventually be born. We don't know what the chain is. Mew is the 'common ancestor of all Pokemon', but where does it fit in with everything else? We know that it was after Arceus, Dialga, Palkia, and Giratina, at least. If I had to guess, I'd say after those four, Yveltal and Xerneas were born. Xerneas went first in what would become the cycle, creating the first bits of life, which are probably the other legendaries, the first one being Mew.
Yveltal destroys, Xerneas restores, the survivors interbreed, etc etc.
The idea that different Pokemon survived and perished from Yveltal's continuous destruction also spurs on the fact that many different Pokemon exist with common traits, like types.
