Today I spent a few hours in Shadow Labyrinth (Heroic) to complete the Trial of the Naaru: Strength quest. This is one out of three quests required before going to Magtheridon Lair to become attuned for Kael’Thas dungeon.
I experienced it—with sweat and pain. I will write up sometime tomorrow Saturday an extensive guide of what you should expect here and how to beat it. Murmur is a real pain in Heroic mode with new abilities. Basically, you have to eat the Deep Breath or else he will start nuking everyone if you go outside the ring—which is what you would naturally do in normal mode. Make sure you don’t bring undergeared people there if PUGing … it is hardcore.