>Say you're in charge of a gen 1 PC port, a gen 1 sequel, a gen 1 rereremake
I would have a series of requirements in-game that can be fulfilled to get Mew, but the existance of this quest is never directly acknowledged or made apparent, similar to the Regi puzzle walls or Rotom in DPPT, so you have to piece it together yourself (or have a billion youtube videos spoiling it for you days after the game comes out) with maybe a few random notes in the Pokemon mansion to give you hints if you know what you're looking for.
Random example:
>after catching/defeating Mewtwo in Cerluean cave during the postgame as normal, there's a hidden item left where Mewtwo was standing (detectible with dowsing rod like normal, but not immediately apparent)
>it's the Berserk Gene, although unlike Gen 2 it doesnt have any apparent effect when held
>if given to a Ditto, it acts as if Ditto is about to evolve and flashes Mew's sillouette, but it's a fakeout and the evolution automatically stops half-way through as if it was cancelled
>this unlocks the 151st slot in your dex, with Mew's sillouette and unknown data
>next time you evaluate your dex with Oak, instead of telling you generic advice for completing you dex, he asks if you knew that Mr Fuji used to be a researcher like him
>if you go talk to Mr Fuji he dismisses you and says his days of research are something he's long buried
>going back to the Pokemon Tower and checking a statue at the top reveals a hidden cache and gives you 'Professor Fuji's keycard' as a key item
>returning to the mansion and using the keycard somewhere in the basement opens up a few more levels of decrepit laboratory space to navigate
>reachng the end there's a chamber where Mewtwo was created and more research notes on how they planned on finding Mew
>last note has the Old Sea Map attached
>take it to the Vermillion docks and go to Faraway island
>catch mew
