You will need to search everywhere in Sinnoh. Wild Pokemon battles should add most Pokemon to your Pokedex. Trainer battles will help you find some more, especially the gym leaders and the elite four. The rest should come with the flow of the story, such as Dialga, Uxie, Azlef and Mesprit
you have to catch all of the pokemon in diamond or SEE all of the pokemon
See all 150 Sinnoh Pokemon
First you have to find all 150 Pokemon then talk to professer rown and then you p. oak comes and opens it. And you then get the national pokedex.
You have to migrate from GBA to NDS. How about trying the site I've just provided?
You can get the National Pokedex in Diamond when you see all 150 Pokemon, but not necessarily capture them.
See all 150 Pokemon in the Sinnoh Dex and talk to Professor Rowan.
You have to see all 150 Pokemon, you don't have to catch them. After that go to Professor Rowan
there are 150 kinds of Pokemon that you can see and/or obtain. Unless you have friend trade you Pokemon that you can only get in pearl to you, you'll never obtain them all. In Pokemon diamond and pearl all you have to do is see the Pokemon and you get its data unlike the older versions where you have to obtain them.
you have to get the national dex when you see all 150 Pokemon orif you play platinum you will have to see all 210 Pokemon
No all you have to do is SEE the first 150 Pokemon then you shall get the national dex..
get an action replay then get the "poke mod" otherwise known as Pokemon modifier and then find all the Pokemon.
All 150 pokemon are in the game so you dont have to trade for them. BUT IT IS EASYER