By beating the elite for then Beating the champion.
hes is the pokemon league champion
You can't!
in kanto
All in regional dex
you can not get master ball in Pokemon emerald exsept in lotto in the big shop and in the agua cave. PS you can use a code
You get your first Pokemon, then warp back there after beating the Pokemon league.
you ferry there after beating the league with your own Pokemon
You get in on the giant island with the survival area after beating the Pokemon league.
Wow u grimlon u get in to the Pokemon league by beating all the 8 gym leaders. Rrrrrrrrrrrreeeeeeeeeeeeeeeeeeetttttttttttttttaaaaaaaaaaarrrrrrrrrdddddddd!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
Actually, you don't ever need to set foot into the Cave of Origin in Pokemon Emerald after beating the Pokemon League ever again! There is no need nor no reason for you to be there anymore, anyways.
I believe you get him by beating the Pokemon league with mewtwo in your party