After overcoming another puppet of Anankos, you discover the real traitor in your midst.
Before the Battle
There are many treasure chests in this map, but no Chest Keys, so bring some units that know Locktouch if you want to open those chests.
Defeat the Boss
During this battle, Corrin and Azura will have healtiles around themselves wherever they go.
There are many Dragon Veins around this map. Their purpose is to freeze the water, preventing reinforcements from coming out of that water. The ice will melt after five turns.
Make your way around the edges of the room, freezing the puddles and killing enemies as you go. There are many treasure chests around the room that you can loot as you progress.
When you are ready, you can easily defeat the boss unit using armorslayer or beast killer weapons.