You catch them in the solaceon ruins in solaceon town
I dont know what happen in diamond, but in platinum you can catch ! and ? unowns.
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first you have to beat the champion then go to the unknown/fourth lake then go to the cave and you will be in a maze and if you look hard enough you will find it.
You are not able to catch the regis in Diamond. You can catch them in the Game Boy Advance version of Pokemon Emerald.
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.
You can't. You can only catch it in pearl and platinum.
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Pearl/Diamond-Lv.30Platinum- unknown
You cannot catch rayquaza in diamond
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You can't catch one.You need to trade it from Pokemon Diamond/Pearl/Platinum version
you can catch a lot of unknown Pokemon A-Z