Shifts into different stances during the fight.

Stance of Fright
Stance of Dread
Stance of Terror
Stance of Thule (at 25%)

At 25% stance of Thule is a large defensive buff. He will avoid much dmg and be extremely resistant to Magical and Mental attacks. Getting as much debuffs back on him at this point is the key to this fight. Dispatch and Shaman debuffs are important.

Everything up to 25% is pretty easy.

If tanking him in the pit where he stands you will have to deal with the stance of fright which will spawn little flowers that need to be killed otherwise they fear your raid.

Mob can be pulled up the stairs between Gnorbl's and Gnillaw's room to avoid that fear attack. You wanna stay max range from him at all possible as he does have a knockback ability.