Light up the Bonfire with your special action key skill. Kill the spawning Icebrood Elementals or use control effects like Pull to prevent them from extinguishing it and throw Firewood into the fire to keep it burning. The stronger the bonfire, the faster the ice wall will melt - usually after around 75 seconds.

If you gain too many stacks of Hypothermia (one every 5 seconds), reset them by standing at the bonfire.

When there are only a few percent remaining, go near the fire to leave combat and pre-equip Executioner Axe Toy to be faster on the bridge.

Elemental Source

At the start of the fight, light up the five bonfires to remove the 10 stacks of Rime Shield from the boss. Each stack reduces its damage taken by 10%.

Every 25%, the Elemental Source casts Wind Gust (icy projectiles) which makes the bonfires loose health. If a bonfire goes down, you will need to throw firewood into it and light it up again using your special action key.

With reflects and high DPS you can simply burst the boss before any bonfire expires. Note that the Elemental Source is a structure so no potion or sigil will work on it.

Forest

After the Elemental Source is destroyed, everyone except the fastest player can /gg and wait for the next checkpoint at the cave to trigger. Mobility skills and Endless Choya Piñata Tonic / Executioner Axe Toy are very good here, skip videos below.

Shaman Lornarr Dragonseeker

Stack Might before the final boss. Make sure to dodge into the boss room to avoid getting Chilled from the icy bolts.

He gains 3 stacks of Rime Shield reducing his incoming damage from the three respawning Corrupted Ice Crystals, destroy them before focusing the Shaman.

At 75%, 50% and 25% you will need to kill a summoned Icebrood Effigy. Dodge every red circle during the fight and break the defiance bars immediately to prevent mechanics.

At 25% the boss transforms into a powerful bear. It’s CC bar should be broken and killed quickly. The animation on the side gives an idea about how the encounter.