By Spleener on 2008/03/28 (Patch 2.4.0)
Apparently, every mob in Sunwell Plateau has this. It's basically a band-aid for the fact that Blizz screwed up the way tank gear scaled so that now people can get ridiculous amounts of avoidance.
It was either this or make bosses hit so hard that they'll either miss or one-shot a tank. I'd say they made a good call here.
Question from the Community:
Regarding the Sunwell radiance aura (minus 20% to dodge) in Sunwell Plateau, is this still active and is there any plans for it to be removed?
There are no plans to remove this aura and it should remain permanent.