I was pretty sure most people knew how to kill the boss in STK without getting hit but then i grouped with a ton of folks that didn't know the TRICK. So here it is.
First you need casters with magic missile or adamantine ranged weapons. The boss has a huge damage resist but spells seem to get through just fine. SO bringing a magic missile wand is nice too.
Ok have a rogue enter the boss room and then run into the corner. Everyone else needs to stay behind the gate that closes so dont go into the room. Now the rogue needs to hide in shadows in the corner of the room. Just hang out untill the gate opens back up and then run back out of the room and into the hallway. Have everyone stay back aways and fire away with your magic missiles or other ranged weapons that are made of adamantine.
The boss will just stand there trying to get into the hall but he is too big so you can pummel him without him hitting anyone. If he starts throwing things at you just stand behind the rocks in the back of the hallway or have a fighter put up a shield to block the incoming rocks.