There is no definate way to beat the Elite Four for sure (unless you use a Sableye or a Spiritomb Lv. 100 hacked to have the ability Wonder Guard :P), you just have to find a strategy and work hard at it. Unless your Pokemon are pure awesome (Like mine are, they swept through the E4 piece of cake)
no
keep trying to beat them
there are no specific Pokemon that can automatically beat the elite four. HOWEVER, ( i speak from experience) i beat the elite four with one Pokemon whitch was Samurott. i suggest using Samurott 2. hope i helped! :) - Raven
Yes, you cant go pass Nimbasa or Opelucid city until you beat the elite four, N, and ghestis.
you have to beat the elite four
You either fight N or fight the champion
You have to beat the elite four. Then beat Ghetsis and N.
You can fight Cynthia in black or white after you beat the elite four and ask for him/her at GTS.
wifi battles battle subway dress up do elite four again link battle (if fiends have pokemon black or white)
After you beat the Elite Four and go into the Plasma Castle.
You beat the Elite Four and Champion, but their are other things you can still do.
You just get legendary Pokemon I guess