i think you get a mystery gift or an event

YOU NEED A NINTENDO 64

you have to get a wireless adapter to open the mystery gift and you have to give the wonder mail to a man upstairs in the pkeheal center.then you get the old sea chart from the man.then go to the ship where you travel on and tell them you want to go to the place on the map.they will send you there and you will see Mew.you have to keep following it until you get in a battle with it.to catch it i would recamend putting it to sleep then weaken it a little until it has a little life left and make sure it is still asleep.then throw either a ultra ball or save you master ball and you have the legendary MEW.

ok well to obtain the old sea chart you have needed to go to an event in Japan or USA which like nobody did so to spread it around you use ur wireless adapter and then spread it around or another way to get it is using a gameshark or Action replay use the codes to obtain it or you could just use the code that when u next get into a battle with a wild pokemon it will be Mew or any other pokemon that you set using action replay or gameshark..

i don't have a clue in hell