After you finish the main game go to white forest/black city. At the left of white forest/black city there is a building. Its the transfer lab. Go in there to Migrate. You need 2ds(any model, dsi,3ds,dslite). Pokemon White or Black. Pokemon SoulSilver, HeartGold, Diamond, Pearl, Platinum. In the B/W go into the transfer lab and talk to the guy at the end. In the ds that has SS/HG/Pt/D/P in it go to download play(in the ds/dsi/3ds menu).Follow the onscreen directions. You cannot migrate pokemon that know HMs or hold items(actually you can migrate pokemon with items, but the items will not be migrated in B&W only the pokemon). You cannot migrate eggs. Only 6 pokemon per time.
When you go to castelia city you can talk at a guy in a building. He will ask you to tell him a phrase. The phrase is Everyone Happy and Simple Connection. When you enter the phrase correctly you will unlock the relocator. At the menu of the game you can select ''Relocator''. With the relocator you can transfer Raiku, Suicune, Entei, Celebi(all of these pokemon have to be the event ones) and the item Lock Capsule(event item). When you transfer raiku,suicune,entei you unlock the pokemon Zoroark. When you transfer Celebi you unlock the pokemon Zorua. When you transfer the Lock Capsule you have to take it to a guy named Mr.Lock(located in castelia city), he will unlock it and he will give you the TM95 Snarl.