How do you get so much Pokemon on Pokemon Diamond?
First, you find a Pokemon you don't have. Then you weaken it with attacks. Then, you spam pokeballs until you catch. Repeat until you have so much Pokemon.
You can't, because Pokemon black was made after Pokemon diamond, Pokemon diamond wouldn't be able to recognise any of the new Pokemon. So to solve this problem they stopped all trading from black to any other game apart from white. You can however get your Pokemon from diamond to black by using the poke transfer, yet you need to have won the league for the first time to be able to do this.
if you mean can you get Pokemon from pearl and diamond and trade them to ruby so you can get diamond and pearl Pokemon on ruby. then no you can not. but you can migrate ruby Pokemon. you put the Pokemon in ruby that you want to put on diamond or pearl in the PC. save it turn off. then go to diamond and migrate them. must be in ds at the same time. pal…