I just 5 shammied almost all of MC. I can kill everything in the entire instance with the exception of baron geddon as he will put a magic debuf on you that burns 400 mana every 3 seconds. I skipped him and killed everything else, then brought in a DK tank friend, and it was ridiculously easy, but I was forced to wait 5 minutes for the debuff to wear off. With water shield and all mana totems, I could barely regen any mana even out of combat. I wonder if something like restorative potion would work to remove the magic debuf. All the other fights where a simple dps race. Kinda funny, he got knocked back by ragnaros rather quickly and died in the lava, and I was still able to burn him down from 90% well before he submerged.
Can't you ground this debuff with 5 grounding totems?

Quote Originally Posted by Wowhead.com
Ignite Mana: Debuffs random players within 45 yards with a debuff that continually burns mana and deal fire as long as mana is burned. Should be removed with Dispel Magic.
This suggests that this spell can be grounded but maybe I am just wrong here ...