I think this has been the first time I've ever read something in FL and said, "that's a bad sentence." Specifically, one of the lines is:

"A tributary of the Writhing River coils nearby. You make your way through the envenomed mists, following the first sibilant, then thunderous, hissing of it."

If you remove some of the descriptive words, the second sentence can be reduced to "you make your way through the mists, following the hissing of it." Which doesn't make sense. I get that they meant to say "you follow the hissing of the river," but the antecedent rule makes it look like you're following the hissing of the mists, not the river.

And I don't particularly care one way or another about ending sentences with a preposition, but "following the (adjective) of it" doesn't ever sound good: "an ambulance zips by, its sirens on full blast; you follow the wailing of it"? Just, no.

It's also somewhat confusing to read "following the first sibilant," as on initial parsing the sentence seems to be using first as an adjective for sibilant as a noun, I.E. "throw the ball to the first baseman."

There are so many better ways the sentence(s) could have been written:

"A tributary of the Writhing River coils nearby, its banks obscured by envenomed mists. You make your way towards it, following its sibilant, then thunderous, hissing. "A tributary of the Writhing River coils nearby. Envenomed mists obscure it from sight, but you find your way by following the sound of its hissing, which increases from sibilant to thunderous as you near." Etc, etc.