=you first have to complete the sinnoh dex,this is not that hard.==however the national dex is,YOU HAVE TO CATCH EVERY POKEMON THERE IS!!!!!!!!!!!!!!== you HAVE to trade and migrate,==hope it helped!==^_^=
You must see/catch all the Pokemon in the Sinnoh dex and then talk to Professor Rowan.
No, there is not a Pokedex after the National Pokedex in Pokemon Diamond Version.
you compete the sinnoh dex.
What you have to do is catch all the Pokemon from all the other regions(complete national dex.
In the sinnoh dex,it is Feebas In the national dex,Omanyte
Beat the Champion Cynthia
You can get the national dex from the professor after you have seen every Pokemon in sinnoh.
you cant get every Pokemon be4 you get the national dex
In Sinnoh Dex it's unown and in national dex it's tangela.
No. It's part of the Sinnoh dex.
On your Diamond you have to have the national dex, but in your GBA game you don't.
find him in the ND(national dex)