You need a grass type, a fire type, a water type, an ice type, your legendary and a ghost or dark pokemon.
FireGrassWaterGhost or DarkElectricRock or Grond
There aren't specific Pokemon for battles.You should use your strongest Pokemon.
There is are no certain Pokemon needed to defeat the elite four. Just use your strongest Pokemon.
the best Pokemon in diamond is arceus, but you have to use action replay or wi-fi mystery gift
you go to the Pokemon center in hearthome city and talk to nurse joy after you've beaten the elite four
You can beat the elite four with any combination of Pokemon, so the choice is up to you. Try getting your starter, Floatzel, Starraptor, Dialga, and two other Pokemon of your choice.
You have to use your poke radar when you beat the elite four at routes 225 and 226.
You can't catch Dialga in Pokemon White. After you beat the the Elite 4, you can use the PokeTransfer to receive a Dialga from Pokemon Diamond, or Platnium.
beat the elite 4 get boy ralts evolve it into kirlia and use dawn stone on it ;D
pokemon diamond, because its up to date
The best way is to give a weaker Pokemon a exp. share then keep beating the elite four. If you can't beat the elite four then you might want to use the vs. seeker and look for trianers to battle.
you could use xp share in the elite 4. or get battling with vs seeker and use rare candies.