https://pokeconspiracy.fandom.com/wiki/Mew-Arceus_Relationship basedo n wat this wiki said, Mew theory: Mew and Arceus existed at the same time, both were gods of the pokemon world. Arceus made pokemon and Mew made humans. ... Celebi, having control over time, sends mew to the time of chaos, producing the egg from which Arceus came from, effectively creating the apparent paradox of pokemon origin.
