Pokemon Platinum how to beat Cynthia in the Elite four?

well what i did is i got a luxray and staraptor both with intimidate and switched them back and forth 2 or 3 times for like spiritomb and garchomp etc. and then brought out a powerhouse and slaughtered them but i used like 40 revives oh by the way dont listen to john spiritomb isnt weak against fighting because he is part ghost and ghost cancels fighting spiritomb has no weaknesses