Creeping Death

Necrotic Spell, Tier 7, 3 Actions, AoE

Reach: 8. Damage: 4d20. If this kills the creature, it violently erupts and you MUST deal the same amount of damage to another creature within 8 spaces of it that has not yet been damaged by this effect. Repeat until a creature survives this damage or no other creatures are within Reach. Upcast: +1d20 damage.

From Core Rules