2 ways, cheat (hack, glitch...whatever) , or trade.
Go to Cerulean Cave. To get there, you must get the ruby and the sapphire and get the national dex.
You have to trade it from a profile that already has it from Leafgreen, Firered, Ruby, Emerald, or Sapphire.
you have to have beaten the elite four and you have to find the ruby and sapphire for the machine in the Pokemon center on one island. then you can enter cerulean cave and get mewtwo
Mewtwo isn't in Sapphire. It is in Leaf Green and Fire Red.
u cant loser
you can not get mewtwo in Pokemon ruby,sapphire,leafgreen or fire you can only get him on pearl ,dimond and platinum
you cant get mew in leaf green without cheating or trading but you could get mewtwo in the ceruelean cave and to get access to go in you have to return Sapphire to bill s friend
you have to get the ruby and the sapphire in the seveii islands you get the sapphire in the dotted hole and you get the ruby in mount ember this can only be done if you have beaten the elite four and after you get the ruby and sapphire you can get mewtwo by going in the cerulan cave. hope this helps! :)
Mew isn't in Leaf Green. Mewtwo on the other hand is. So basically you can't.
You can only get mewtwo by trading from Leaf Green or Fire Red.
seriously thtas impossible get an action replay
You can't catch mewtwo in pearl, but you can transfer one through pal park if you have one in firered,leafgreen,ruby,sapphire, or emerald. Or you could use cheats to catch mewtwo in pearl