Obsidian Sanctum

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 drake 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.

A 10 and 25-player version of this raid exists.

Lore
In the wake of the Nexus War, Alexstrasza tasked her children with rooting out any danger and treachery within the Wyrmrest Accord. They quickly located a clutch of twilight dragon eggs within the Obsidian Sanctum. With their resources already strained in dealing with the Scourge and the blue dragonflight, Alexstrasza's consort, Korialstrasz, has sent word of the eggs to Dalaran's Council of Six in the hopes that able-bodied adventurers can enter the sanctum and destroy the twisted progeny of Deathwing.

Dungeon denizens

 * Black dragon (one, Sartharion)
 * Black dragonspawn
 * Black drakonids
 * Fire elementals
 * Twilight drakes (three, Shadron, Tenebron, and Vesperon)
 * Twilight dragon whelps

Mobs

 * Acolyte of Shadron
 * Acolyte of Vesperon
 * Disciple of Shadron
 * Disciple of Vesperon
 * Lava Blaze
 * Onyx Blaze Mistress
 * Onyx Brood General
 * Onyx Flight Captain
 * Onyx Sanctum Guardian
 * Sartharion Twilight Whelp
 * Twilight Whelp