Your favorite boss encounter

I know this might sound silly but the boss encounter I enjoyed the most was The Lich King. Reason for this is because of all the events that occur in one fight it is entertaining , fun , and tests your skills. More encounters need to be like this for the reason being it makes the game more interactive !

Let us hear what your's is ^_^

I liked Icehowl, and LK aswell, Icehowl required some SKILL, get hit by the bugger and you got a handful of raiders on your case in vent, and your dead. And you screwed up the raid. So ya, Kept me under pressure the whole damn time. LK had some cool mechanics, such as Defile and Necrotic Plague, Although if you got those two down your set, unless people don't deepz the Valk's.
I was a holy priest and got sent into Frostmourne..... -_-