>>37933857I'm surprised this still stumps people so much, though admittedly there's no confirmed right answer. Bulbasaur and Mew are right out, as Bulbasaur's is only a number and Mew was first neither in canon nor concept.
It gets questionable when you get to Arceus and Rhydon. But Arceus was said to be born from chaos, and I think there's reason to believe Unown are in fact the chaotic force that created Him in the first place. Even Arceus needs to use the Unown as a medium through which to create new legendaries; He unites them, but it would make no sense to create that medium if He could create everything by himself in the first place. Though it's only a theory, this leaves Rhydon as the only choice that is without a doubt, the actual first Pokémon in some legitimate regard.
This also possibly answers OP; Arceus is a good sport, and doesn't use Unown to assist, which would be extra 'mons on a team.
