As the bell rings, a burst of necrotic energy ripples out in a 20-foot-radius sphere from a point you can see within range. Each creature in that area must make a Wisdom saving throw. On a failed save, the creature is marked with necrotic energy for the duration. If a marked creature is reduced to 0 hit points or dies before the spell ends, you regain hit points equal to 2d8 + your spellcasting ability modifier. Alternatively, you can choose for one ally you can see within range to regain the hit points instead.