i believe you catch em all...or go face the elite four again.as you do that you can look all over the land for the three dogs.........you can find out what they are because they are mysterious......
Catch 'em all
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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
No you cant get Mew on leaf green, but you can get Mewtwo in Cerulean Cave.
No trade one from firered or leafgreen.
you beat the elit four again
Use Action Replay
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to catch suicune,mewtwo,raikou and entei
I believe you face the Elite 4 again.
Master Ball
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