The knights have discovered the entrance to one of the heretics' key hiding places. You enter it in search of Iceheart.
How to Unlock
The Snowcloak dungeon is unlocked by the level 50 Main Scenario Quest The Path of the Righteous.
Get a Tiny Key
Follow the path and kill the enemies that you encounter. There will also be large shards of ice that fall from above and cast a circle attack centered on itself.
You eventually encounter a White Bear. Kill it and take the Tiny Key that it drops. Then check on the Door to Silence to proceed.
Kill the Ice Bomb and the two Snowcloak Wolves to clear the path to the next area.
The Tank should turn Wandil away from the rest of the party. Wandil will periodically use Ice Guillotine, a cone attack.
After taking some damage, Wandil will cast Snow Drift, which has a delayed effect. You need to keep moving to avoid getting a stacking Frozen status when the Snow Drift attack lands. If you get four stacks of this, you will get the Deep Freeze buff and be unable to move.
Wandil will sometimes cast Cold Wave, placing several circle attack markers in the area, which will give you a stack of Frozen if you are standing in it when the cast bar finishes.
Throughout the battle, Frost Bombs will appear. If they are not killed before they self-destruct by casting Hypothermal Combustion, the party will get a stack of Frozen.
Wandil itself can also cast Hypothermal Combustion as a room-wide attack.
When Wandil's health is about 33%, it will periodically cast Tundra, which creates a ring of ice around the edge. Standing in this ring of ice for too long will cause you to gain a stack of Frozen.
As you proceed through the next area, avoid standing in the windy areas, or you will get the Frostbite status, which causes damage over time until you leave the windy area.
Yeti will periodically cast Buffet, a wide cone attack.
Yeti can cast Northerlies, a room-wide attack that damages all party members.
After Northerlies, Yeti will make snowballs appear, and will make one or more of the snowballs larger. Keep your distance from the large snowballs, as they will cast large circle attacks around themselves. The smaller snowballs cast small circle attacks centered on the snowballs, so don't stand too close to them.
Yeti sometimes casts Spin, which starts with a circle attack centered on the boss, then adds a donut attack around the edge that overlaps slightly with the center attack. Stay out of range of the inital circle attack, then as soon as it disappears, go into the safe area in the center to avoid the donut attack.
This is followed by Frozen Spike, which places a circle marker on all players. Move away from other players to avoid overlapping your circle markers.
Finger of the Apostate
As you proceed through this area, you will eventually reach a dead end, and several waves of enemies will attack. The final enemy is a Snowclops. Defeating it will open the path to the next area.
Kill all of the Dove Aevises in the next area, and one of them will drop a Finger of the Apostate. Take it, then check on the Door to Oblivion and proceed into the next area.
Fenrir will sometimes cast Thousand-year Storm, which damages all players.
Fenrir will cast Howling Moon, then four circle attack markers will appear, and icicles will fall into them. Then Fenrir will begin casting Lunar Cry. Hide behind one of the icicles to avoid the attack. As soon as Lunar Cry has finished casting, quickly run away from the icicles, because they will cast a large circle attack around themselves before they disappear. If you get hit by it, you will be afflicted with the Deep Freeze status.
Fenrir will sometimes cast Ecliptic Bite, a high-damage attack on the tank.
Fenrir will sometimes target a random player with Heavensward Roar, a long cone attack. Be sure not to be in front of Fenrir when you see it casting Heavensward Roar.
The next time icicles appear, three of them will have red cracks in them. Hide behind the one that does not have any cracks, because the cracked icicles will be destroyed and cast circle attacks centered on themselves before the Lunar Cry attack.
Completing the Quest
Defeating Fenrir will complete one of the quest objectives for the Main Scenario Quest The Path of the Righteous.