I almost died laughing. Ok Arceus created Mew(unless it descended from space like everyone think) And several other legendaries including Groudon, Kyogre and Rayuaza to create land, water and control weather respectively.
Arceus also created Dialga, Palkia and Giratina. I think it also created the dragon that split into Zekrom and Reshiram. So yea Arceus DID create Mew.
As for some of the jokers here that think Mew gave birth to all the Pokemon, it would be hard to imagine Mew giving birth to Groudon's egg. It would also be hard to imagine Mew giving birth to Arceus in spite of how weak it is.