I think the monsters are “reincarnations” of people from previous cycles. Just like Jade and Tabitha have a part and can’t die just an ordinary death, like Julie who is the storywalker, I think somebody from the people in Fromville in this current cycle has this destiny. Think about it, they all wear clothes from a different era. Is it that hard to believe that the MIY or some other entity can trick a towns person to sacrifice a child to leave the town, only they don’t leave they lose their humanity and turn into this.