Galgann Firehammer

Shadowforge and Stonevault camps
Clear Galgann Firehammer's Shadowforge camp before moving into Grimlok's cavern. Handle the Geologists before their fire overlaps Galgann's vulnerability effects. At Grimlok, separate the basilisk and spellcasters from the boss fight rather than allowing reflection, stuns and fire vulnerability to interfere with the lightning casts.

Galgann Firehammer
Elite HumanoidGalgann Firehammer punishes overlapping Fire attacks while Amplify Flames and Flame Lash make their target more vulnerable to them.
Abilities

Fire Nova
Inflicts Fire damage to nearby enemies.
Fire Nova hits nearby players. Keep healers and ranged attackers outside the melee group so the nova does not damage everyone carrying a fire vulnerability.

Flame Lash
Flame Lash lowers Fire resistance. Remove its magic effect when possible before another Fire Nova or Geologist cast hits the same player.

Amplify Flames
Increases the Fire damage taken by an enemy by 100 for 30 seconds.
Dispel Amplify Flames from its victim before the next fire hit; it increases Fire damage taken rather than dealing damage by itself.

Flame Shock
Flame Shock leaves continuing Fire damage. Remove it when possible, especially while its target also has Amplify Flames or reduced Fire resistance.
Tank- Keep Galgann and his Geologists in the cleared camp while the guards are removed. Leave the healer outside Fire Nova's nearby damage rather than pulling Galgann onto their casting position.
Healer- Prioritize removing Amplify Flames and Flame Lash's resistance reduction. Heal Flame Shock's victim while remaining outside the melee group and clear Flame Spike's burning area before resuming casts.
Damage- Control or defeat the Shadowforge Geologists before concentrating on Galgann. Interrupt Flame Spike and give the healer time to remove fire vulnerability instead of taking avoidable Fire Nova hits.