What makes it special
PC Gamer distinguishes ordinary vampire progression from Vrakhir blood: most vampire skills arrive through regular vampire progression, while specific abilities become available when Coen drinks Vrakhir blood.
Abilities
How Vrakhir Blood Unlocks Vampire Abilities
Where the special blood comes from and why it is different from ordinary progression.
The source lists three boss-linked abilities: Ambrus grants Scarlet Shield, Bakir grants Shadowstorm, and Xanthe grants Blood Surge when their blood is consumed. It says certain Murohn encounters and selected quests can also provide vials.
Decide before consuming
The guide reports that this blood raises Corruption substantially and can unlock an ability without skill points. Check the current quest context and your desired character direction before treating a vial as disposable loot. The final article should clearly label this as a mechanics spoiler.