Bile Vessels are essentially Blasphemous‘ equivalent of the Estus Flask in Dark Souls.
You start out with two active Bile Vessels in Blasphemous, and each one allows you to restore an amount of health with just the push of a button – handy for when you find yourself close to death. To refill them, you simply have to visit a Prie Dieu. Although they’re also refilled when you die.
You can increase your number of Bile Vessels in Blasphemous, however, allowing you to restore more health and stay in the fight for longer. But they don’t come easy.
To unlock an additional Bile Vessel, you first need to find an empty Bile Vessel. You can find them by simply exploring and completing side quests, and the vendor might also sell you one or two. Once you have an empty Bile Vessel, you then need to take it to a fountain of blood. Once you’ve found one, it will be displayed on the map with a symbol that looks like a jar of blood.
Interact with a fountain of blood while you have an empty Bile Vessel in your inventory and you’ll be asked if you want to fill it for a set amount of Tears of Atonement. It starts at just 500 Tears of Atonement, but the cost increases every time you turn an empty Bile Vessel into a full one.
When you don’t have an empty Bile Vessel in your inventory, visiting fountains of blood can still be beneficial. For a small cost, they allow you to refill your health and any used Bile Vessels. Useful when you’re not close to a Prie Dieu.