Forerunner of Fate

Forerunner of Fate is a kill quest given by Argent. It requires killing a Boss mob.

How To Achieve
Harbinger is a high-tier boss mob, wielding the most powerful ranged attacks only outmatched by The Grimm Reaper. Be careful, keep moving, and preferably, use ranged items that can attack quickly, like Dagons or Bows enchanted with Quick Draw or used with the Mutant Skeleton Chestplate.

Harbinger can also see through blocks, but cannot destroy them. But he may be able to corner you, so be careful with your decisions.