Chapter 21B: Eternal Stairway

You'll start off surrounded by Faceless in this map. Your objective is to reach the escape point with all units intact. Each of the Faceless monsters here have Camilla's area-of-effect skill, Savage Blow. Any enemy within two spaces will lose up to 20% HP after any Combat they initiate. That said, as much as possible, get the combat initiative and keep your healers ready. The Stoneborn are ranged monsters that can even disable your character's movement and leave you open for attack.

Having units (usually the offsprings) with area heal ability (Azura's Amaterasu passive ability) should help a lot in this battle. Also, f you have any “Blessed” weapons, equip them to your main units since these weapons deal extra damage against the Faceless. As much as possible, don't pair too many units, especially your healers since you'll need their extra actions. It is also recommended to use the dragon veins along the way to freeze the enemies on the spot for a turn.

Mobility will be the key here to initiate Combat and to quickly eliminate the stoneborns. Fliers will do the trick here so if you have strong, reliable flier units, make sure to bring them and pair them with powerful supports that you can switch to do the close-range combat. At the first turn, activate the nearest dragon vein and start moving forth. Some parts of the path are blocked by rubble so make sure to study your immediate area first before moving your unit.

As you make your way up, reinforcements will appear to the north and south. It will be beneficial for you to use the dragon veins every turn on your way up. This way, none of the faceless can chase after you and you can initiate Combat. Just remember to heal up whenever necessary, especially when the stoneborn's projectiles connect. Once you've reached the top, make sure that you eliminate as much faceless as you can so no one gets left behind. Your most powerful units should guard the rear and let your other units reach the escape point first. You also have to defeat the boss faceless since it has an Arms Scroll. Once all your units escape, the mission will be complete.