you can't catch metang in Pokemon, but you can catch the devolution, beldum by talking to dawn's sister in Sandgem town (you have to beat the elite 4 and champion first) there is only 1 Pokemon per day so do it daily or ask her and if it's not it change the time on your ds to 11:59pm wait 1 min and then ask again
You cannot catch a Metang in Pokemon Diamond. To get one, you can evolve a Beldum.
You can't catch Metang in emerald. You can only get Beldum, and then you can evolve it into Metang.
You can't catch one.You need to trade it from Pokemon Diamond/Pearl/Platinum version
Darkrai is a dark type of Pokemon. You can catch one in Pokemon Diamond version on Newmoon Island but you need a membership card.
You cannot catch a slowpoke,slowbro or slowking on diamond version. You can on Pokemon pearl version though.
5
You are not able to catch the regis in Diamond. You can catch them in the Game Boy Advance version of Pokemon Emerald.
Unfortunately, you can't catch a Red Gyardos is Pokemon diamond, but you can catch one in Pokemon Heart Gold or Soul Silver. It'll be at Lake of Rage.
use ultra balls
You can't yet.
You need to trade or migrate it.
Sorry to say, but no, you cannot catch a Palkia on Diamond version. You catch a Dialga on diamond, and Palkia on pearl. You would have to trade to get one.