Dragons of Nightmare

The Emerald Dream was entrusted to Ysera for safekeeping, and the mightiest of her green dragon brood were assigned to stand watch over four portals that connected directly to Azeroth. But even before the Cataclysm, these dragons began to show signs of corruption. Now, the path to the Nightmare's core runs through the dragons' lair.
Overview
Ysondre shares health with Emeriss, Lethon, and Taerar. She begins the fight alongside the nightmare of one of her former cohorts. When Ysondre reaches 70% health remaining, the nightmare takes to the skies and a new one emerges from a nearby portal. Upon reaching 40% health remaining, the nightmare dragon in the air lands and the one on the ground takes to the air.
Damage Dealers
Be sure to switch targets to prevent [Slumbering Nightmare] from triggering. Try not to stand directly behind the dragons so as to not be struck by [Tail Lash]. Stand within the [Nightmare Bloom] to prevent Dread Horrors from spawning.
Healers
Be sure to switch targets to prevent [Slumbering Nightmare] from triggering. Quickly dispel [Defiled Vines] from allies so that they can escape the resulting [Defiled Eruption]. Stand within the [Nightmare Bloom] to prevent Dread Horrors from spawning.
Tanks
Be sure to switch targets to prevent [Slumbering Nightmare] from triggering. Face the dragons away allies so they don't get hit by [Corrupted Breath].