Seat of Lords

Seat of Lords is a prison beneath Azshara that became active recently. every immortal lord became imprisoned here, both from Azeroth and Outland. This raid is available to whoever has the most bases captured in Azshara Crater. Each boss unlocks after the original version of the fight has been beaten.

Thunderaan - Lord of Thunder (world boss)
Found inside The Burning Wastes.

Ragnaros - Lord of Fire (tier 1)
Found inside Frostfire Caverns

Al'akir - Lord of Wind (world boss)
Found inside Polaris, not always up.

Ahune - Lord of Frost (tier 4)
Found inside Battle for Teldrassil.

Murmur - Lord of Sound (tier 5)
Found inside Auchindoun.

Therazane - Earthmother (world boss)
Found inside Maraudon.

Kraaj - Lord of Sand (rare boss)
Found inside Uldum.

Neptulon - Lord of Water (world boss)
Found inside Azshara.

Naxaron - Lord of Fear (tier 4)
Found inside Naxxramas.

Xarn - Lord of Death (tier 7)
Found inside Karazhan.