Could you say in which particular room this mirror can appear in? I know you've stated it involves the Red Book but I haven't found anywhere to use it. I've looked in both the Library, Basement, and Cabin Basement in desperation since those are the only areas I know that that bookshelves and that floor texture. I even made sure to have True Sight on after the mirror swap. This might be due to a flag missing on my doomed file or I'm missing something incredibly obvious or complicated.