Yagluth is a boss with 10,000 health.
It resists pierce and fire; poison does nothing to it at all. Blunt and slash land at full damage, so that is what to bring.
Its hardest hit is meteors at 120 fire and 40 blunt, out of 3 attacks.
Some of what it throws is elemental, so fire and lightning resistance is worth having.
Of everything craftable, 
Lightning Strike, 
Frostfire Sledge and 
Frostfire Greatsword put the most damage through what it resists.
It always drops 
Yagluth Trophy and 
Torn Spirit.
Yagluth's altar is a giant stone hand reaching out of the Plains. His vegvisir hides in Stonehenge formations and spawns rarely, so you may stumble on the altar first. Five 
Fuling Totems summon him; raid fuling villages to collect them.
Yagluth digs himself out of the ground slowly when summoned and he is vulnerable the whole time, so spend that window swinging. After that he fights with fire: a rotating beam, meteor volleys and a lightning nova around his fist. 
Fire Resistance Barley Wine turns lethal hits into survivable ones, and his own aura stops the rain, so do not count on being wet. He is very resistant to pierce; put the bow away and bring blunt, slash or frost. 
Frostner is a favorite here for a reason. Strafe sideways through the beam and sprint clear of the red glow before the meteors land.
The flat damage bonus applies to every damage type, which makes this the default power for boss fights.
He drops the Torn Spirit. It builds the 
Wisp Fountain, and without wisps the Mistlands stays a wall of fog.
With devcommands enabled, this spawns Yagluth in front of you. The third number is the level: 3 spawns a 2-star.
Creature ID: GoblinKing · all console commands and IDs