Lyxen
Great Old One
But IMO it would make more sense that the healing be based on the number of creatures taking damage. Then it would be more like a life siphoning thing (necormatic).
I thought about this, but then the problem is that it becomes too easy to abuse. Also, considering the very abstract nature of hit points and the fact at a hit point does not mean the same thing from one creature to the next, I think I understand why they choose to deal fixed dice damage to a number of creatures and a different system for the healed one, so that people do not think about that "conversion".