So, side topic.
Magic Items that are references to things not in the game (such as the Nessus tag).
I brought this up in another thread, so I'll start with it here. The Vacuous Grimoire, which was just a shot at the 3PP Arduin Grimoire.
Description-
A book of this sort is totally impossible to tell from a normal one, although if a detect magic spell is cost, there will be a
magical aura noted. Any character who opens the work and reads so much as a single glyph therein must make 2 saving throws versus magic. The first is to determine if 1 point of intelligence is lost or not, the second is to find if 2 points of wisdom are lost. Once opened and read, the vacuous grimoire remains, and it must be burned to be rid of it after first casting a remove curse spell. If the tome is placed with other books, its appearance will instantly alter to conform to one of the other works it is amongst.
That's right. Gygax was telling you that the book tried to look just like a D&D book, but it made you stupid.