With a Masterball
Only if you have a code breaker and the master code for ruby plus the mew and mewtwo code
1. you cant catch mewtwo on ruby emerald or saphire<spelling mistake> you can migrate the mewtwo you catch on leafgreen or firered to migrate to platinum
ANSWER 1:Mewtwo appears only in Fire Red and Leaf Green. You can catch him in either of those games and then trade him to Pokemon Ruby.sorry mate its impossible only way is to trade like this guy said (: (: (: (: (: (: (:ANSWER 2:I regret to tell you that you cannot catch Mewtwo in Ruby. You can only catch Mewtwo in FireRed or LeafGreen. (You can use cheats to get it but it wouldn't be as fun).Mewtwo is at Level 70 in LeafGreen and FireRed so use an Ultra Ball/Timer Ball/Master Ball.If you need/want a Mewtwo you can trade Mewtwo into your Ruby/Sapphire/Emerald Game.
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
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.
You can't. You'd have to trade it from a Pokemon FireRed or LeafGreen game.
Unfortunatley, you cannot catch Mewtwo in Pokemon Ruby/Saphirre/Emerald. But you can trade it in from Firered/Leafgreen. Also, instead of asking on Answers for Pokemon questions, just go to Serebii.net
first u have to beat the elite four and get the ruby and Sapphire then you can get into the cave to catch mewtwo
give him the ruby on island six, then you can catch mew and mewtwo
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
You can't catch Mewtwo in Pokemon Diamond and pearl and also platinum. But you can catch Mewtwo in heartgold and soul silver
you have to beat the league national dex ruby sapphire (not the game ruby sapphire) then go to to ceraluen city then the guy in the cave guy is gone