How do you get the national pokedexs on Pokemon Diamond version?

Answer 1

After you see all of the Pokemon in your pokedex, show ur pokedex to professor Rowan and I'm not sure exactly what happens next, because I haven't reached that part yet, but I think he just says good job and hands you the national pokedex! If you don't know how to see all of the Pokemon, just battle as many of the trainers as you can and don't forget Dialga who is at the top of Mt. Coronet. I have already caught it! Hope this helps a lot! Pokemon diamond version for sure