Pokemon X and Y Walkthrough: Elite Four Drasna
Drasna uses Dragon-type Pokemon, three of which have a secondary type. The common weaknesses all four share are Ice and Dragon. The easiest move to use against her Pokemon is Ice Beam. You should have already received TM 13 from Wulfric in the Snowbelle City Gym. Altaria and Noivern actually take quadruple damage from Ice Beam because of their secondary Flying types. Dragalge might be able to withstand a Special Ice attack like Ice Beam because of its high Special Defense. The Pokemon to really look out for on Drasna's team is Druddigon. It has a very high Attack stat and is not shy to use Dragon Tail for massive damage. Fortunately, it doesn't use any moves like Dragon Dance to power up any further.
Elite Four Drasna