help plz

To get the national dex you have to see every Pokemon in the sinnoh dex including dialga and palkia, but not including manaphy, phione etc... You cannot obtain palkia in diamond, but you can get the pokedex entry necessary for the national dex from a lady in celestic town. You can find comprehensive lists of all the Pokemon in the sinnoh dex from various sites on the internet giving the number and where it can be seen. There are a few common oness people miss. Usually number 114 is unown and lumineon and finneon are commonly missed as well. But if you have explored all areas of all towns and fought all the trainers you shuold get the national dex right away soon.

In order to obtain the National Pokedex, you have to either see, or capture every Pokemon in the Sinnoh Region. Yes, that means that you must see all 150 Pokemon before you can obtain the National Pokedex from Professor Rowan. If you need some help with a certain Pokemon, or a location on a few of the Pokemon, then do not hesitate to ask here for help. Unfortunately, no, you cannot get Palkia in Pokemon diamond. You can however, see a picture of Palkia that will be added to your Pokedex. Go back to Celestic Town and talk to the old lady in the cave, she will show you the picture. Hope this helps.

To see alot of the Pokemon, not in the game to catch, you will have to fight all the trainers. If you battle them it will show thier Pokemon in the pokedex. You have to have seen all 150 pokemon.