Armor-Piercing Rounds

Armor-Piercing Rounds is an item in Risk of Rain 2. It increases your damage by 20% (+20% per stack) against Bosses and Hordes of Many spawned by the Teleporter, as well as Special Bosses and the Umbra from the Artifact of Vengeance. It reflects this by changing the color of your damage numbers, if they are enabled, to orange when you are damaging an applicable boss. Such targets will also have red health bars instead of the usual yellow bars.

This item does not give you a damage bonus against boss monsters that are spawned randomly by the environment in the late game.