this one's simple.
during phase 2 of Galakras in siege of orgrimmar, any death knight can effectively ignore the stacking debuff from flames of galakrond.
if you use anti-magic shell directly before the first cast (when the ball of flame would apply the debuff), you won't receive any stacks of Flames of Galakrond from the first cast or any other casts of Flames of Galakrond for that fight. you don't even need to use anti-magic shell again, the debuff just won't appear. it effectively makes phase 2 a single tank fight with a blood DK and significantly reduces damage taken by all DKs during phase 2.
i'll get screenshots once i'm in there again. hard to prove with anything short of a video, though, which i am unable to make.