you can. first you have to get the national dex after beating the elite four. to get the national dex you have to see all 150 Pokemon in sinnoh, then go to prof rowan. prof oak will then come and will tell you about the pal park on route 221. Go there and talk to the person at the counter. he will explain the rest
Not Every Single one
you can get one in Pokemon Platinum or in Pokemon Pearl then trade it to diamond
you have to do your ds
You have to do single battles
you need to go on Google.com and type in "wild Pokemon modifier" and you put the code in your action replay then you can get every single Pokemon in diamond!
u get national dex
u hav to see every single Pokemon
you get it when you see every single Pokemon in Diamond or Pearl, then go and speak to proffeser rownan
Anorith Evolves into Armaldo at level 40. This is the same as every single fossil pokemon in every game
Double Battle and single would be Groudon and Thyplosion first and Kyogreo and Wailord second, single is any Pokemon with Recover I recomend a team of Deoxes.
Ummm..... in the unknown cave near solaceon town (if that's how you spell it)
Unless you have a Gameshark or Action Replay or other means of filling your Pokedex, you must transfer Pokemon over from a Pokemon Gameboy game via Pal Park.