This achievement pertains to the hard mode version of the General Vezax encounter. During the General fight you will have a permanant debuff called Aura of Despair. This removes all forms of mana regeneration. There will be a total of 8 Saronite Vapors that will spawn throughout the fight and once they are killed they form clouds on the ground that will restore mana to whomever stands in it at the cost of health. It is not much health, but the longer you stand, the more it takes away. If you do not kill any of the vapors they will merge into a Saronite Animus. This is an add with 2 million health and gives the debuff Profound Darkness. Vezax also gains Void Barrier which will make him immune to damage until the Animus is killed. If you have a Holy Paladin healing, it's best to keep him with the melee group so he/she doesn't have to move very often. Try using Shadow Protection pots to help mitigate the damage from Profound Darkness and try using all damage reduction spells on the tank during this time.