How do you get the the national dex in Pokemon Diamond?

Answer 1

To get the national dex in diamond, you must see, not catch , all 150 Sinnoh Pokemon.

AnswerBy viewing and/or catching all of the Pokemon in Sinohh.

Answer 2

This feat requires only two major steps, although you will need to do some work.

Step 1: After obtaining your Sinnoh Pokedex, you must have seen (you don't have to capture) all 150 different Pokemon in the Sinnoh Region (excluding Manaphy)

Step 2: You must have defeated the Elite Four. By the time you reach and defeated them, you should have seen more than 135 different Pokemon.

Step 3: After completing your Sinnoh Pokedex and beating the Elite Four, head to Sandgem Town and into Prof. Rowan's Lab.

Step 4: Talk to Prof. Rowan and he will congratulate you on completing your Pokedex. Not long after will Prof. Oak from the Kanto Region come and upgrade your Sinnoh Pokedex to the National Pokedex!