it's fake.
You can't. You have to trade from someone from Pokemon Diamond to get it. If you can trade from Diamond...
Trade with someone that has Pokemon pearl.
trade with someone that has Pokemon diamond
yes
ask someone at a Pokemon place
oh ya theres a code for that go on to Google.com and type in Pokemon diamon cheat codes it will work
you can trade with someone that has a dialga in pokemon diamond
No way.... Someone hacked!
Get it in a trade from someone else, or pal park.
by killing someone
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.
he is in jublife. if i am wrong someone else will provide an answer