As with Lifeblood Heart, this charm is useful if the player has a playstyle focused on Spells, as it will allow them to use more of their SOUL on casting rather than healing. However, it is the most difficult Lifeblood charm to obtain.
Arguably the best Lifeblood charm, as it provides twice as many masks as Lifeblood Heart with only one extra notch cost, and does not turn all masks into Lifeblood, unlike Joni's Blessing, allowing for healing if necessary. While having 9 masks, Lifeblood Core grants the same number of masks as Joni's Blessing.
How to Acquire
On the left wall of the Abyss is a door that will only open when having 15 or more Lifeblood masks. This can be reached either through killing Lifeseeds or through the Lifeblood Heart, Fragile/Unbreakable Heart and Joni's Blessing charms. Joni's Blessing also converts the extra health from Fragile Heart into Lifeblood masks. Dreamgate can be used to warp to the door without obstacles.
The charm is found sitting on a dais at the end of the chamber.
There is also an Arcane Egg in the same area. Once Lifeblood Core is picked up, the Knight will be immediately ejected from the room and the door will become permanently closed, so it is recommended to pick up the Arcane Egg first and then the charm.
Charm Interactions and Combo Tips
Stacks with both Lifeblood Heart and Lifeblood Core.
Stacks with both Joni's Blessing and Lifeblood Core.
Grubberfly's Elegy only counts mask health as full health, so by using Lifeblood health, taking damage will not remove Grubberfly's Elegy's effect.