You can only get it through migration from your FireRed/LeafGreen GBA game. Then you go to Pal Park and catch it.
Hope that helps xx
You can't catch mewtwo in Pokemon diamond. It's better if you use Action replay code.
You can't catch Mewtwo in Pokemon Diamond and pearl and also platinum. But you can catch Mewtwo in heartgold and soul silver
You can't catch mewtwo in Pokemon diamond because its not available in the game. if you want it you either get it by a friend or a wifi event which i seriouscly doubt.
you cant catch mewtwo in Pokemon platinum peral diamond you can in Pokemon heart gold and solsilver in canalave cave
You can't catch Mewtwo in-game in Pokemon Diamond.
Mewtwo is not obtainable in Pokemon DPPt. Trade it over from another game or AR.
No two Pokemon make mewtwo ,you must catch it in firered or leafgreen and if you want you can migerate it to diamond or pearl.
You can not catch mewtwo in the wild on pokemon diamond, you can only get it by trading with someone on the GTS or someone you know. The other way is by pal parking the pokemon from fire red or leaf green to your game.
how do you catch a mewtwo on Pokemon platinum
well you can but you can't catch Pokemon in the game so you have to download it from Pokemon diamond,pearl,or plantinum.
Palkia, Lugia, Dialga, Deoxys, Mewtwo, and Mew
yes,mewtwo is in Pokemon dimond/pearl