In the cave there is a big machine with two pillars. The Kill Switches are on the pillars... left first. After each Kill Switch is flipped you will be attacked. After the second switch you fight Stormlord Casimir. When he is very nearly dead he runs to the middle of the cave and tosses up a ward while freeing the two trolls from theirs. Kill the trolls. In the center of the machine there is now a third Kill Switch. Flip it and Casimir's ward drops, then so does he.