Ichor Bullet

Ichor bullets inflict the Ichor Debuff to enemies, decreasing their defense by 20 points, which effectively can increase the damage from the bullet an additional 10 hit points from its base value of 13, totaling the effective damage of up to 23.

Tips
When fighting Bosses, it is possible to add the vantage of the Ichor Debuff to other bullets, to do so the player should alternate bullets in the inventory or ammo slots. For example one slot with 1-10 Ichor Bullets and the next slot with 100 Crystal Bullets, then repeat this slot alternation as necessary to archive the required amount of Bullets to kill the Boss. The amount to put in the slot of the main Bullets should be enough for the gun to use them all in the time that lasts the Ichor Debuff effect (15 seconds).

History
Trivia

They aren't crafted from empty bullets even they are hardmode bullets