Pokemon X and Y Walkthrough: Pokemon League
Before taking on the Elite Four and Champion, know that you can't visit a Pokemon Center after you start. You will either defeat all five trainers or fail and try again. For this reason, be sure to stock up on Hyper Potions and Revives. Malva, the Fire-type member of the Elite Four, gives you the low-down. You can choose to battle the Elite Four in any order.
Dragonmark Chamber (Dragon)
Ironworks Chamber (Steel)
Blazing Chamber (Fire)
Flood Chamber (Water)