Giant Spiders will accost you on the Sundermount. They only have a melee attack, so keep your distance as you attack. Continue onward to the Dalish encampment.
Meet with the Keeper and check out some of the wares in the camp.
Head up the mountain. You will find Merrill on the mountainside. She's another mage, and she's adept at lightning attacks and hexes. She can't join your party right away, but she will be an important attacking mage later on. Continue up the road.
Corpses will rise from the ground and attack on the way to the cave. They are exceptionally brittle, with most of their punch coming from the element of surprise when they appear.
Giant spiders put in an encore appearance once you enter the cave. As before, keep your distance so that they can't bring their fangs to bear.
Several Shades and a Shadow Warrior await near the exit to the south. They will strike near the chokepoint created by the stairs, so run down and try take out the Shades at the bottom. Continue out onto the mountain and make your way to the altar.
Two Arcane Horrors and a Shadow Warrior attack with numerous Skeleton Archers and Corpses after passing through the barrier at the mountain summit. Complete the quest by walking up the summit and watching the scene that follows.