(italics mine)Necromantic Neuro-Link
Arcane Feedback Terminated
Negative Energy Plane
16d12 Continuous Duty
12d8 Intermittent Duty
I believe that 12d8 "intermittent duty" refers to Redcloak in some way, since it's his job to keep Xykon on full HP. Neither Harm nor any of the Inflict spells work like that though. Maybe it refers to Redcloak's hit dice at the time?