"AND THE FABLES OF DOOM"
In this episode, Jake gushed over the annotated copy of "Paradise Lost" in the antique book section, but Jenkins promised he didn’t want to know who annotated it.
I think it's O'Bvious who could be the only one knowledgeable enough to have annotated it - the only TV character who was actually there at the time of the Fall....
So I can see this reference as a viable link between 'The Librarians' and 'Lucifer'.
And actually, it could be a reference to any TV show that depicted Lucifer, no matter the recasting. There is no Zonk because Lucifer would have the ability to alter his appearance, as has been shown numerous times.....
BCnU... in Hell!