Thing in the Ice
Tamiyo's Journal - "Entry 434: There's more to Avacyn's madness . . ."
Avacyn, the Purifier
Anguished Unmaking - "Sorin had created Avacyn, so it was a cruelty beyond imagining, a pain beyond description, that it fell upon him to end her forever."
Ultra Pro - Standard CCG - Shadows over Innistrad - Nahiri