reposting from sdc just to give context for Avent as seen in prior Mewtwo post.
Advent is the First Mew and the First Pokemon (one of three, with Arceus and MissingNo being the other two components of it). All other Mew are its descendants, and are varying degrees weaker depending on how far removed they are from the Advent- though all of them are still very much worth the title of Mythical Pokemon. Though there's not that many left- the purpose of Mews always was to evolve into something else, after all.
Advent and MissingNo came into being as fully formed adults, while Arceus matured over time. Because Arceus got a more complete understanding of life through being the only one to experience childhood, it was the one which created the world and most everything needed for it to function, while it entrusted Advent to handle populating its creation. Since Advent looked after it as it grew, it trusted Advent to be able to watch after the world it created once it went to sleep, as it maintaining the existence of this world takes a lot of energy.
... At least, that's what MissingNo's been told. It can't really remember any of this for itself. But it HAS seen Advent, and its pretty sure Advent is the mew from the story. Probably? Well, just in case, MissingNo's been keeping an eye on the world for Arceus, or whatever made it, so that it knows at least Something is.
"Advent" - The arrival of a notable person, thing, or event. Something which worked out well for me, as the name started as me simply deriving (Ad)am and E(ve).
Advent's design is based on the Ancient Mew card.
