Mostly by battling all of the trainers to see palkia go to an old lady in celestia town and she will show you it
need to see all Pokemon that you can see in the sinnoh region (216) and then speak to the professor and he'll give you the national dex.after that u can catch lagandarys like heatran regigigas...;)
The only way you can see all the Pokemon on diamond is by going into the GTS and global trade different Pokemon.
you have to catch all of the pokemon in diamond or SEE all of the pokemon
you have to see all the Pokemon in sinnoh.
you have to see all the Pokemon in the pokedeks
You just need to SEE all the pokemon.
No, you cannot see every Pokémon in the National Dex in Pokémon Diamond however you can see every Pokémon in the regional Sinnoh Dex in Pokémon Diamond.
u have to go to the battle park
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.
the Pokemon in diamond are sinnoh Pokemon i suggest http://Pokemon.marriland.com/diamond_pearl/pokedex to see all of them
you have to see all the Pokemon on the sinodex then prof rowan gives it to you
all u need is the national pokedex in pearl or diamond to import them u must have it