Nefarian Down!

[savaughn]

The question is, what was wrong with the encounter that required a hotfix.  SO far the only theory I saw was that Nefarian didn't use any of his abilities, and acted very similar to the Onyxia encounter.
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Ask and ye shall receive.

The encounter had pathing issues, apparently. There were a number of places you could stand that would cause the various mobs (drakanoids, skeles, Nefarian) to go into evade mode that would effectively take them out of combat.

So... check this, you could crowd control the entire encounter by selectively aggroing mobs and setting them back and forth between evade mode. There's no question this was an exploit. Blizz did the right thing with the hotfix in my book.