For all intents and purposes, Mew is effectively written out of its canon with the introduction of Arceus. What is still canon is that Mew is believed to have the genetic composition of all Pokemon, but that doesn't mean every Pokemon originated from it.
YOU WANT SOME FUNERAL TO GO WITH THAT CAKE? why aren't you laughing at me? everything i say is funny and adorable
Other mews were like "hold up-you a llama now?" And "Arceus" was like "yeah, now you become bulbsasaur, you can be rhydon..." And etc, forcing some mews to change shape and thus Arceus created (almost) all pokemon, even itself, just not mew or mewtwo, as some guys made mewtwo.
SSB4 dream roster: http://imgur.com/DfdocHN.png 45/50 characters---I support for Echo type pkmon gen 7 This is my flame shield.