In order to catch Registeel in Pokemon diamond, you need to have gotten a level 100 Regigias from a mystery event. This mystery event has passed, so you can no longer get Registeel in Pokemon diamond, unless a friend trades you the mystery event Registeel. The only other way to get Registeel is to trade him from Pokemon emerald, ruby, or sapphire.
I think you meant regigigas, to catch it you have to have the three golems, reiice reirock reisteel from the other versions.
You cannot catch Celebi in Pokemon Diamond.
yes, you can catch Pokemon in Pokemon diamond
neither of them is better, they are both the same, but in diamond, you catch dialga, and in pearl, you catch palkia, and you can catch different Pokemon in each game for example: you can catch this Pokemon in diamond, but not pearl but: you can catch this different Pokemon in pearl, but not diamond
You can catch makuhita in the fighting area in Pokemon diamond
How do you get a cherrim in Pokemon diamond.
ucant catch misdreavus in diamond
You cannot catch a Metang in Pokemon Diamond. To get one, you can evolve a Beldum.
You can't catch a Lugia anywhere in Pokemon Diamond.
Nosepass is a swarm Pokemon on Pokemon diamond
you can catch a pikachu in the Pokemon mansion.
You can not catch a manaphy on Pokemon diamond. you must trade it somehow on a Pokemon rangers game.