Spellcasting focus. Requires attunement by a spellcaster.

A rubbery black facsimile of a human heart that pulses as if alive and exudes a dark miasma in a 5-foot radius aura around itself. Whispering voices can sometimes be heard within the area, subtly urging creatures towards evil acts.

Attunement

The heart must be held against your chest for 8 hours of uninterrupted meditation during which time you are shown incomprehensible cosmic horrors. Good aligned characters cannot attune to this item. At the end of the duration you must make a DC 20 Intelligence saving throw.

On a failed save the heart releases a burst of thick black ichor causing you to take 4d6 necrotic damage and 2 levels of exhaustion. If you fail to attune you cannot attempt to do so again until you have finished a long rest. On a successful save you attune to the heart. While attuned to the heart you gain the following features.

Weavesense

You sense the direction and distance to the heart at all times. This effect ends if another creature attunes to it.

Dark Magic

You gain knowledge of Dark spells which you can cast with your available spell slots. The heart must be held in the hand to cast these spells.

Heart of Darkness

You are resistant to necrotic damage and immune to the frightened condition while the heart is in your possession.

Symbiosis

Immediately after you finish a long rest, you must feed half of your remaining Hit Dice to the heart (round up) or take 1 level of exhaustion. Additionally, when a humanoid that you can see dies within 30 feet of you, you can use your reaction to regain 1d4 expended Hit Dice. The heart can’t be used this way again until the next dawn.