The Awiergan Scrolls: Second Aspect

Acquisition
The Awiergan Scrolls: Second Aspect is acquired upon finding the scroll in Sundermount.

Walkthrough
Upon entering Sundermount, head through the Dalish Camp and up the mountain towards Sundermount Passage. Just before you reach Sundermount Passage you will come across some ruins. The scroll is located behind one of the walls at the ruins. Your journal will update telling you a new Hidden Lair has opened. The Hidden Lair can be found by going through the Sundermount Passage to the Mountain Graveyard. Be careful once you reach the graveyard, after passing it and reaching the Hidden Lair you will encounter 1 named Undead Bysmor and 2 named Revenants, Beacon and Gifre. This is the hardest battle of the 3.

Beacon and Gifre are Revenants as you remember them from Dragon Age: Origins -- very powerful and punishing against any party, so this fight can be tough even on Normal difficulty. On Hard, you'll want a strategy; on Nightmare, you'll need one ...

Pulling strategy:
Exploit: If executed properly, this strategy is more-or-less an exploit of the Dragon Age II combat mechanics, because after pulling and defeating each mob, combat will reset. If it won't hurt your ego, the easiest way to approach any battle is to pull each mob one-by-one.

Before leaving the graveyard and shrine, instruct your party to hold, then send your tank to lead the way towards the Hidden Lair. Slowly round the corner until Bysmor comes into view; once he aggroes on you, run back towards the party. Once you and your mob are safely around the corner and in range of the rest of your party, DPS him down. Rinse; repeat.

"Stand up" strategy
If you prefer a "straight up" fight against all the mobs, the #1 point of advice is to not group your ranged DPS together, because Beacon and Gifre will both do a Mass Pull for massive AoE damage. The #2 point of advice is to not let your squishies pull aggro, because they can get one-shot at range.

(Preferred location: Graveyard)  The easiest place to handle all of the mobs is in the graveyard, because it gives your party room to spread out around them. Use the above strategy of holding your party back at the Shrine, but send your tank northeast until Gifre comes into view -- then hightail it back to the Graveyard.

(Suboptimal location: The narrow paths)  If the battle is to be made in the narrow paths, pull everything into the southern 'bend' of the path. Send one (or two) ranged DPS'ers east of the mobs towards the Hidden Lair and leave one ranged DPS'er west on the path to the shrine. (On Hard and Nightmare, you'll likely have one of your party members one-shotted early on if you fight in the path.)

Wherever the battle goes down, once you've positioned your ranged DPS'ers apart from each other, aggro everything onto your tank and DPS Bysmor down as close to death as possible. (If done well, Bysmor should be alone for a good 10 seconds of the DPS phase.) Corrall Bysmor near Beacon and Gifre, then cast Walking Bomb as you finish him off. Bysmor's explosion will cause roughly 70% damage against Beacon and Gifre!

If your Walking Bomb on Bysmor hits both Revenants, the rest of the battle should be fairly straight-forward as long as you keep up aggro and heals on your tank. Try to repeat the Walking Bomb tactic against the remaining Revenants if time and healing allows.

If your Walking Bomb only hits one of the Revenants, DPS the weak one down but bide your time until Walking Bomb is available again, then repeat the Walking Bomb as used for Bysmor. (If Anders is casting Walking Bomb, repeatedly use Martyr until it is off cooldown.)

If you happen to fail with the Walking Bomb on Bysmor, it's not necessarily over, but it might as well be. Keep aggro and healing on your tank and make sure you hit the Walking Bomb against the final Revenant. Fighting all three mobs consecutively at full strength is ... fun. ;)

Result
After killing the encounters (Bysmor, Beacon and Gifre) your journal will update stating you have completed the quest.

Rewards
Bysmor drops a random ornate level item and about 30 silver. Beacon drops The Celebrant Gifre only drops about 50 silver.