Essence of the Red - A very nifty buff while fighting Vael. All players receive extreme mana / energy / rage generation, essentially having unlimited mana / energy / rage. It only lasts up to 3 minutes for each attempt, so better be killing him within the time limit.
Burning Adrenaline - This is the nasty debuff that you should watch out for. The tank with the highest aggro, and one random mana user will be selected periodically and be given Burning Adrenaline. While this is in effect, all spells are buffed and become instant cast. But, while under its effect, the victim's health will continue to decrease at a rapid pace. And if the Burning Adrenaline expires and the victim is still alive, it will cause the person to explode, doing massive damage to everyone around him. Mana users who receive it should immediately run to the nearest corner, and do appropriate damage to Vael before they die.
Fire Nova - Vael hits everyone around him with a fire AoE, which disrupts casting time if it is not resisted. High amount of fire resistance should help you resist it, and avoid having your cast time to be held back.
Cleave - Vael has a cleave, so melee and healers need to make sure they are positioned appropriately to avoid that. Melee should be just behind his front legs, and healers should be at max distance while still being able to reach with their healing spells (Prayer of Healing or Holy Nova).
Fire Breath - Massive fire AoE damage breathed from the front of Vael. This ability should really only be hitting the tank unless Vael gets loose into the raid, or he turns to the raid and applies Burning Adrenaline to someone then does this ability immediately while he is still facing the raid.
Tail Swipe - Vael does a tail swipe to anyone who is at his tail. This ability knocks the person away, so be sure to avoid his tail at all cost.