From Guild Wars 2 Wiki
— In-game description
- Dropped by any Branded creature while this section of the achievement is active.
- You will need 10 Branded Residue in order for Yasna to accept them.
- You must actually speak to Yasna first, before these will start dropping.
- This will drop from any Branded creatures in Path of Fire maps, not just the ones in the Domain of Istan.