You can't catch one.You need to trade it from Pokemon Diamond/Pearl/Platinum version
No, you cannot catch Darkrai in Pokemon White.
at the end of the game
You catch them with a ultra ball
Yes you can catch Reshiram in Pokemon black and you can catch zekrom in Pokemon white hope it helped.
You can't catch entei in Pokemon black he is on a different version
No.
you cant
You can't catch Dialga in Pokemon Black. You need to trade for it or transfer it from the older Pokemon DS games.
You can't get Darkrai in Pokemon Heartgold. You have to trade it from Diamond, Pearl, or Platinum.
Throw a pokeball at it.
Pokemon Black Version and Pokemon White Version are the same game, except for the pokemon that are available to catch and for certain areas.
you go to calave island go to the inn and sleep and there he is