Greetings! Root of Nightmares only drops Spoils on repeated clears on characters that have already run it that week. So say, after the first clear on your Warlock, within the same week, if your Warlock were to run RoN again, you would get Spoils in place of the usual loot drops. Also, the secret hidden chests will drop Spoils along with an additional loot drop, and those are limited to one loot drop per character, per week.