An Soul Return Grimiore in form of soul skill. Consider your own question answered. Good for files that have staying power and fights by attrition. I originally thought about solar kingdom but they get bent over too easily unless its a lvl 4 rush meh.
Its second life for zombies. lots of 1 copys left on field? activate that ss and get all ur zombies back whee along with supporters like mad priestess broken priest , etc.
Although i've been honestly thinking about giving it a try but all the BKRs is too busy hiding from my Ridrea.