Blood Crystal

Wondrous item, uncommon (requires attunement by a creature not of lawful good alignment)

You can use a bonus action to touch this crystal against the body of a creature of CR 1/2 or greater, that has died within the past minute, to gain one charge on it (the creature must have blood).

This item can hold a maximum of 20 charges. You can use your action to expend all charges this item holds, destroy it, and deal necrotic damage equal to 1d4 for each charge consumed to a creature you can see within 60 feet of you.