Circle of Death (5.5e Patch)

Negative energy ripples out in a 60-foot-radius Sphere from a point you choose within range. Each creature in that area makes a Constitution saving throw. On a failed save, a creature takes 8d8 Necrotic damage, and can't regain Hit Points until the end of your next turn. During that time, it also temporarily gains 2 level of the Exhaustion condition. On a successful save, the target takes half as much damage only.

Using a Higher-Level Spell Slot. The damage increases by 2d8 for each spell slot level above 6.