Recapture the Greatwall
Defeat the Wights
Enter the Greatwall Encampment and you’ll have to deal with a couple of armored cyclops and several snow harpies in the immediate courtyard. Take out all the harpies first then concentrate in taking out one cyclops at a time. Take note that it’s possible for the two cyclops to damage each other when they’re near each other so use that to your advantage too.
Explore the eastern area of the hold’s first floor. Quickly save the knight nearby to have him open up the locked spiral staircase that leads to more treasure and items. Make your way to the second floor and engage the Chimera. The same tactics in taking it down still applies and the crates in the room contain curatives. There’s also a ballista nearby that you can use.
The frightened knight will open the door, allowing you to proceed further. Loot the chests in the room he’s in and continue until you reach another knight-in-distress beside the stairs. Save him to open this alternate staircase and loot the extra items inside. If you failed to rescue the knight, you can access this alternate room by throwing an explosive barrel on its weakened wall.
Proceed to the third floor and defeat a heavy skeleton knight. Loot the nearby chests and save your game. The boss fight is just ahead so heal up your party as necessary. When ready, head out and face the wights and their army of skeleton warriors.
These wights are airborne most of the time so the only way of dealing real damage is by attacking them with magic and ranged attacks. If you’re a dedicated melee character, concentrate on eliminating the summoned skeleton warriors to force them to lower their altitude and summon more again.
These enemies are weak against holy attacks so bringing a mage with the capability to enchant weapons with holy magic will help a lot in dealing with these powerful necromancers. You have to be careful of Maelstrom; this spell deals a lot of damage and will fling your characters helplessly on the air, damaging you continuously while the spell is active and will also cause tremendous damage when you hit the ground.
For the tedious sidequest “From a Different Sky”, you can find the Badge of Vows 40 on an arch in the northern side floor. You have to dislodge it using a ranged attack (which is another great way of temporarily changing vocations for this battle) to get that badge. Take note that this is the only way to reach this; if you failed to get it and you complete the quest/ the battle ended, you’ll have to attempt again in another playthrough.
After defeating the wights, watch the following scenes and the quest will be complete.