Malygos has roughly 6,972,000 health in normal difficulty, and 19,523,000 health in heroic difficulty.
Summoning Malygos requires one member of the raid to have either [Key to the Focusing Iris] (10-man) or [Heroic Key to the Focusing Iris] (25-man, though it can also be used for 10-man). Both keys drop off Sapphiron in Naxxramas (10 and 25-man respectively).
Phase 1
Malygos does a frontal physical attack and a frontal cleave. His attack speed is slow, but it does a lot of damage. Unlike other dragon bosses, he does not have a tail swipe.
* Arcane Breath: deals 18850 to 21150 normal, 28275 to 31725 heroic, Arcane damage in a 40-yard cone in front of Malygos. It leaves a debuff which, after 5 seconds, causes the person to explode and deal 9425 to 10575 normal, 18850 to 21150 heroic, Arcane damage to nearby friends.
* Arcane Storm: Fires arcane missiles into the air, which strike a random number of targets for 9425 to 10575 Arcane damage. Malygos will turn to the primary target of this ability when he uses it.
* Vortex: Malygos takes off from the ground and spins up a whirling vortex of Arcane energy, tossing the raid around and dealing 2000 Arcane damage every second for 10 seconds. When Vortex ends, everyone will be dropped around the center of the platform and take up to 10% of their maximum health in falling damage.
* Power Sparks: At regular intervals throughout the encounter, a portal will appear in the empty space away from the platform, between two of the pillars, and spawn a Power Spark. This Power Spark will slowly move towards Malygos and give him a temporary buff upon reaching him which increases all damage done by 50%, unless killed first. When players kill a Power Spark, it will leave a temporary patch of electricity on the ground which will buff players, increasing damage dealt by 50%. This buff will stack. During Vortex, Power Sparks stop moving; however, once you begin to fall from Vortex, they start moving again. Power Sparks can be Death Gripped, snared, rooted, stunned, incapacitated, and so on.
* Enrage: Malygos has a 10-minute enrage timer, at which point his damage is increased by 1000%. This timer carries over across all phases, therefore the entire encounter must be completed within 10 minutes.
Phase 2
Malygos will take to the sky and stops using all of his previous abilities at 50% health. Any Power Sparks that reach him after phase 2 begins will have no effect.
* Arcane Storm: Fires arcane missiles into the air, which strike a random number of targets for 9425 to 10575 Arcane damage.
* Deep Breath: Deals 5000 Arcane damage per second to the whole raid for 5 seconds. Cast at regular intervals. A warning, 'Malygos takes a deep breath,' is given before Malygos uses this. This ability does not effect anyone flying on a disc.
* Power Overload: Purple anti-magic zones will periodically appear on the platform, reducing all magic damage taken while standing inside by 50%. These zones will shrink as they absorb more and more damage, forcing you to move to a newer one. They will knock back players nearby when they spawn.
Nexus Lord
Nexus Lords will spawn at the beginning of phase 2. They stand upon floating discs and descend to the ground. They must be tanked normally and will drop their discs on the ground when they die, allowing melee classes to fly up and engage the Scions of Eternity.
* Arcane Shock: Deals 9425 to 10575 normal, 14138 to 15862 heroic, Arcane damage.
* Haste: Increases movement, casting, and attack speed by 100% for 15 seconds. Can be dispelled.
Scion of Eternity
Scions of Eternity will spawn at the beginning of phase 2. They fly upon floating discs, which puts them out of the melee range of anyone on the platform. They have no aggro table and will periodically cast Arcane Barrage on random targets. When one dies, it will drop its disc to the ground, allowing melee classes to fly up and engage them.
* Arcane Barrage: Deals 14138 to 15862 normal, 16965 to 19035 heroic, Arcane damage to a random target.
Phase 3
Malygos will shatter the platform when all of the Scions of Eternity and Nexus Lords are dead, beginning phase 3. The raid will drop onto red dragons, which will be used to kill Malygos. Malygos stops using all previous abilities in this phase.
* Arcane Pulse: Deals 28275 to 31725 Arcane damage to anyone within 30 yards of Malygos.
* Static Field: Creates a blue, electric-looking orb on a random target. This orb deals 9425 to 10575 Arcane damage per second to anyone within 30 yards of it.
* Surge of Power: Malygos will target a random person and give them a warning that Malygos is focusing on them. Malygos will then shoot a beam at his target, dealing 12000 Arcane damage every half second for 3 seconds, as well as 5000 Arcane damage per second to anyone near the primary target for 5 seconds.