Here's what I don't get: To create a dark fountain, a lightner needs to thrust a weapon into the ground. Not just into whatever - into the earth. King made it clear in chapter 1 that the Knight "pulls the Fountains from the Earth." Every dark fountain we've seen so far has been at ground level. So how could a dark fountain be made in or adjacent to that room in Flower King with the double doors and colored flowers? It's clearly upstairs. A Flower King dark world would only make sense in the main part of the store, or in the basement (which we know is there but we haven't seen yet.)