Build a raised plateau in view of his altar. About 8 raises with the hoe per section. Make the plateau big enough to accommodate a portal back to your base.
Next, build frost arrows. They do substantially more damage than all other arrows, silver included. About 300 arrows should be fine.
Summon the boss, and immediately run up the plateau you constructed. Yagluth, will be unable to path to you and will literally just stand there. Rain arrows on him until he is defeated.