Eye on You
Common52.2%ObjectiveOptionalAnywhere
Defeat the Eye of Cthulhu, an ocular menace who only appears at night.
Your first real boss. It can turn up on its own once you have 200+ HP, or summon it at night with a Suspicious Looking Eye (6 lenses at a Demon/Crimson altar). Preparation beats gear: a long flat arena with campfires, a decent bow or a flail, and keep moving horizontally - phase two charges in straight lines, so sidestep and punish. Drops the ore you want for your next armour tier.