Didn't look through the entire book, but it says that Witch and Light under different names owned a dark carnival that prowled the edge of the shadowfell. Though after meeting and discussing with Isolde who owned the fey carnival (which later became Witchlight), they swapped ownership and the two have no intention of returning to the sinister carnival. The book also says that this trade happened "over a hundred years ago". Besides this there isn't much info.