Consyte's Blessing

This spell was said to be employed by benevolent cultists called Consytes during the Age of Darkness. Though the patron deity of the Consytes has been forgotten, and the cult itself has all but disappeared, their teachings remain. 

Touch one willing creature within range. For the duration, whenever this creature regains hit points, it regains an additional 1d4 + your spellcasting ability modifier in HP. However, you take the same amount of necrotic damage. This damage ignores resistance and immunity to necrotic damage.