Hill suspected it was Rose... Her Spider Weave had been modeled on the Shadow Weave, and back in Gerns World, she had even stolen a piece of the False Weave before leaving.
The other gods of Toril could not afford to offend Shar lightly. But the Spider Queen came from another universe and now lived in the Bottomless Abyss, so she had far less to worry about.
Rose was afraid of Shar, of course... but only because Shar and her followers were far more powerful than the Spider Queen and hers.
So the cunning Rose never opposed Shar openly. Shar might not storm into the Bottomless Abyss to destroy Rose's true body, but wiping out every one of Rose's followers on Toril would be easy.
And Shar guarded her weave even more closely than Mystra guarded hers... Take the one in Gerns World, for example. Rose had intended to carry off the whole thing.
William had learned how to gather up and use the weave so quickly that he must have had an excellent teacher.
The fact that Rose had risked stealing a piece of the False Weave made her ambitions clear... and the Spellplague had handed her the perfect opportunity.
Her famous Spider Weave was, in reality, an endless physical network on the sixty-sixth layer of the Abyss. It was made of spider silk and stone slabs covered in magic arrays, and even housed her followers in the Abyss.
Outside the Abyss, it was a virtual network sustained by faith and fear, less useful than the False Weave William had made. Her believers could draw certain dark spells unique to Rose from it, and those she permitted could use it to send messages or even teleport in person. Anyone who did not worship Rose could not use it at