Breath rune

Breath runes are a form of non-craftable rune that can be used in place of any three blood runes, body runes, or air runes. They have a small chance to drop from many magical NPCs such as Otherworldly beings, but the most popular NPCs to farm them from are Gore elementals, as they have the highest drop rates, and also commonly drop blood runes.

Spells
Breath runes can be used in place of blood, body and air runes for any spells in which they are used, but they can not be used in place of these runes if they are needed in quests.