you get him on fereaway island
So far only 5 games get the opportunity to capture mew in some way: Red version, Blue version, Yellow version, Emerald version and My Pokemon Ranch.
Red version was not made to migrate with emerald.
Emerald can trade with Leaf Green but not Pokemon Red
u cant only emerald
you can't catch mew in Pokemon platinum you can only get it by cheats, mystery gift, migrate from a Game Boy Advance Pokemon game like fire red, leaf green sapphire, ruby, or emerald version.
You can't catch Mewtwo on XD, Colosseum, Ruby, Sapphire or Emerald. Mewtwo can be caught in the Fire Red or Leaf Green Version then traded over to Emerald, Ruby, Sapphire, Colosseum or XD.
Get an Action Replay.
You must first get it from Emerald version and then trade it over. But if you have just Sapphire, you can't get it. you can"t get him but you can get him on gts You can't. You need to get it in another game pak. Fire Red for instance. Capture the Mew in Fire Red or Leaf Green and trade it to sapphire.
you only can get them with cheats (i realy hate that with all that events and cheats =[ )
You can't catch mew at all in any of the games unfortunately. You can only get it through the use of an AR or game shark or stuff like that.
There is no possibility of getting a Mew in Pokemon fire red version.. but it can be obtained through the Action replay code or a Nintendo event....
you have to migrate it from ruby,sapphire,emerald,fire red, or leaf green