I DID IT! I DID IT! I used an ultra cheesy method too!
First I tanked all my guys up with the usual pre-combat spells, then i summoned in two greater drowned deads, a shadowed cyclops, and two earth elementals. Then I flipped the switch and ran for it while the summonings kept the dragon busy. Then i cast Otiluke's Resilient Sphere on one of my characters and positioned them at the base of the stairs. The dragon couldnt get through so I lowered his resistance, emptied my spell book on him and then hit him with about 20 or so necklace of missiles. IT WORKED! Kinda feel let down though... No Carsomyr treasure on the dragon
