This chest spawns after you defeat the Madness of Deathwing encounter.

10 Man Normal
Maw of the Dragonlord
Gurthalak, Voice of the Deeps
Rathrak, the Poisonous Mind
No'Kaled, the Elements of Death
Kiril, Fury of Beasts
Souldrinker
Blade of the Unmaker
Vishanka, Jaws of the Earth
Ti'tahk, the Steps of Time
[Reins of the Blazing Drake]
[Essence of Destruction]
[Elementium Gem Cluster]

10 Man Heroic
[Souldrinker]
Blade of the Unmaker (heroic)
Gurthalak, Voice of the Deeps (heroic)
Maw of the Dragonlord (heroic)
Kiril, Fury of Beasts (heroic)
No'Kaled, the Elements of Death (heroic)
Rathrak, the Poisonous Mind (heroic)
Ti'tahk, the Steps of Time (heroic)
Vishanka, Jaws of the Earth (heroic)
[Life-Binder's Handmaiden]

25 Man Normal
Gurthalak, Voice of the Deeps
Maw of the Dragonlord
No'Kaled, the Elements of Death
Rathrak, the Poisonous Mind
Kiril, Fury of Beasts
Blade of the Unmaker
Souldrinker
Vishanka, Jaws of the Earth
Ti'tahk, the Steps of Time
[Reins of the Blazing Drake]
[Essence of Destruction]
[Elementium Gem Cluster]

25 Man Heroic
Gurthalak, Voice of the Deeps (heroic)
No'Kaled, the Elements of Death (heroic)
Maw of the Dragonlord (heroic)
Rathrak, the Poisonous Mind (heroic)
[Souldrinker]
Kiril, Fury of Beasts (heroic)
Blade of the Unmaker (heroic)
Vishanka, Jaws of the Earth (heroic)
Ti'tahk, the Steps of Time (heroic)
[Life-Binder's Handmaiden]