I could see Xykon casting it on Ochul, Vaarsuvius, or Redcloak(after he becomes aware of Redcloak's betrayal). He's aware that they would be particularly upset at being partially responsible for the death of their kinsmen, and they've made him mad enough to get that personal.
That said I think one genocide is enough for this comic. Doing it again but without the moral lesson seems too dark for Rich.