During the next session, my players will get their hands on a book of prophecy from a temple in the chaos wastes. The book is supposed to be a cryptic tome that the players can use to get guidence and hint about what to do. However, it's not as easy as just opening the book and reading it. The true mening of the prophecy is hidden within the text and is not without its risks to unravel.

So the general idea I have is that they will carry this tome with them and try to consult it for guidance when unsure about where to go or what to do in a general sense. But each attempt to read the book brings with it chances of mental damage.

Has anyone else used forbidden tomes in their games where players could learn usefull stuff from them, but with a high risk? I am thinking of doing something like a Education(Willpower) check where failures lead to stress and Chaos Stars give temporary insanities?

Yes of course, think the Brendan Frasier "Mummy" movie, "You must not read from the book", and generally this is where Call of Cthulhu comes in. A dusty book is potentially more dangerous that whatever is making that moaning sound around corner though also potentially more useful to investigate. You can destroy it to eliminate the risk but at the cost of losing what possible advantage?

Liber Fanatica 4 has some 2nd edition thoughts on this: http://www.liberfanatica.net/LF4download.html

I have done something similar as in "it's a sort of encyclopedia but each time you consult it you are taking a trip down the rabbit hole", but for advantages perhaps you learn a creature trait or just get a special pool of tokens use as "fortune points" and you narrate how this comes from your reading (I did that for consulting some texts about vampires during my Thousand Thrones campaign, a special pool useable only in situations involving vampires or their powers/minions).

Books can amount to Fear or even Terror checks to "learn things you wish you didn't know", and not just one check but a series (one book with enough scary stuff should be enough to drive a reader over the edge into complete madness if they "keep reading" and "keep making bad checks"). You might need Education to figure out what it's saying but that won't help you avoid the insanity threat - in fact ignorance is your best friend on this front, the only time Education helps is when the scary thing is a false claim/prophecy that enough Education and intelligence sees through the compelling argument that is false, so you don't have nightmares after learning that the Emperor is really a vampire.

Books can also, when they are truly ploys of the Ruinous Powers or the product of Necromancers etc., be imbued with Dhar and taint that threatens corruption points.

They can be "focus points" for the attention of a specific daemon or supernatural antagonist so that "every miscast result is really part of that power's plan", or such consulting it triggers progress along a track of its agenda.

There is the Forbidden Tome card for a handout.

Oh, one last point, this should probably be in GM or Houserules section.

Yeah, I should probably have posted this in the GM section. Oh well.

I have ben writing a bit on this and this is what I've got so far:

Remember that this is a bit mcguffin in my adventure and there are tangible rewards to be had by getting information from the book, which is why I bother making the process so complex instead of deciding it with just a single roll.

Make a 5 step tracker. The reader has to get to get to the final step to learn anything usefull.

To make an attempt to move up the tracker, he has to spend an hour reading to make a roll.

If he wishes to stop reading, this requires a Normal Discipline Check.

If he closes the book and attempt to contiue later, nothing will look quite as he remembered it and his last attempt will have been for nothing. For each hour reading, he gets 1 Fatigue.

Hard Education(WillPower)