Obsidian Sanctum guide

The Obsidian Sanctum is the black dragonflight area of the Chamber of Aspects. The entrance is in Dragonblight and accessed via a crack in the ice below Wyrmrest Temple. It holds one raid boss, Sartharion the Onyx Guardian, and his three lieutenants, Shadron, Tenebron, and Vesperon. Raiders may choose to kill all three drakes or leave some combination of them alive. Completing the encounter with one or more drakes up increases both the difficulty and the quality of loot that drops.

Hint: In case you have to corpse run: head north, drop down from the temple, make a 180 degree turn and head into the summoning hall.

Shadron
If left alive, he will apply his aura, Power of Shadron, to the entire raid as long as he is alive, increasing Fire damage taken by 100%.

Tactic: ot, healer and dps (at least 2) should head into portal to kill the add that spawns.

Tenebron
If left alive, she will apply her aura, Power of Tenebron, to the entire raid as long as she is alive, increasing Shadow damage taken by 100%.

Tactic: ot, healer and all dps heads into portal to kill eggs and any whelps that spawn from unkilled eggs. On 10 men normal we don't bother with the eggs, off tank will gather up all whelps and boss should be dead before too many whelps have spawned.

Vesperon
If left alive, he will apply his aura, Power of Vesperon, to the entire raid as long as he is alive, decreasing everyone's maximum health by 25%.

Tactic: ot, healer and all dps heads into portal to kill the add that spawns.

Sartharion

• 7,670,000 HP (25 man), 2,510,100 HP (10 man)
  
• Cleave, fairly weak (35% melee damage). Not likely to one-shot even clothies.
  
• Tail Whip, minor damage, stuns for 2 seconds.
  
• Frontal Fire Breath for 10k (10-man)/12k (25-man)
  
• Will cast Pyrobuffet at anyone outside the area of his platform, rapidly killing them. Brief dips in the lava will generally not trigger Pyrobuffet.
  
• At 10% he goes into a sort of soft enrage, summoning what looks like 5-10 of the elemental adds.

His immediate area is surrounded by a small moat of lava. The north (right) / south (left) sides of this lava spawn lava waves by Sartharion during his emotes every 30 seconds. See layout/positioning images below for details. Everyone must stay in the layout to prevent the Pyrobuffet.

Lava Waves
At certain intervals, a raid warning will appear saying, "The lava surrounding Sartharion churns!" Lava waves will then spawn that originate from the left or right of the encounter area. These waves place a minor DoT on any players caught in them, so players should move to the gaps between them. The location of the gaps is predictable depending on the side that the waves originate from. They are huge, obvious, and slow-moving, however, so players should have no trouble watching for them and moving out of their way.

Sartharion's Fire elemental Adds
Health: 65165 (25), ~26,000 (10)
These adds are summoned every ?s in groups of 2-4 to be offtanked. If these adds are hit by the lava waves they will enrage to deal 400% more damage, so ~800 becomes 4k, modified by Shadron's aura. Adds should be moved out of the path of the Lava Strikes. DPS will have to drop these as priority after they spawn and are picked up by the OT. The offtank must be careful using area of effect taunts when gathering the adds because Sartharion is not immune to taunt.


For details on positioning and lots more info about doing the encounter with 1-3 lieutenants alive see wowwiki