B is for BOOKS
There is a cumulative 1-in-12 chance per dungeon level that a found book has Special Properties.
Random Special Properties of Books
1 The book is CURSED, and reading it activates the curse.
2 Reading the book makes the reader permanently immune to the effect of one random spell. If the spell is beneficial, the character must succeed a saving throw vs. spells in order to allow themselves to be affected by it.
3 Biological monograph on local monster species reveals one heretofore unanticipated combat vulnerability.
4 Extremely extended family trees for ruling families of several demihuman and humanoid races reveals their previously unknown shared evolutionary origins.
5 Field manual with extensive marginalia on a random skill (as thief) provides a +1 (or +17%) bonus to the first 1d6 attempts to use that skill. There is a flat 1-in-12 chance per skill use that this bonus will become permanent. Each skill use requires 1 exploration turn of consultation before the attempt.
6 Encyclopedic volume on a random area of expertise (as a sage) provides answers to the first 1d12 questions on that topic. Due to verbosity and inadequate indexing, each question takes 4 hours to look up an answer.
7 Over-hyped divination manual with ludicrous illustrations of author's cosmic power actually does foretell the future. The first 1d6 readers each gain a random fortune after staying up all night reading it.
8 Ineffectual-looking but surprisingly potent self-help manual provides tips and exercises to be a better person. After 1d6 weeks of use, the reader gains a permanent +1d6 to a random ability score. Subsequent readers spend 1d12 weeks to discover they get no benefit at all, and become convinced that original player character has been duped by a flim-flam author.
9 Extensive theological treatise sufficient to allow a player character to scribe scrolls to banish, bind, dismiss, ensnare, summon, or torment one random demon god of the underworld, plus one such scroll already completed.
10 Schematic allowing the player characters to assemble one random piece of anti-diluvean technology.
11 Pre-apocalyptic novel is a guaranteed best-seller. Every merchant the player character meet is going to want to buy the "rare surface edition" and put it into mass production. Every NPC the characters meet will be reading (or re-reading) the book and will want to talk of nothing else. There is a flat 1 in 6 chance each week that it's finally been replaced by some other underworld FASHION.
12 First-hand historical account of previous apocalypse implicates ancestors of the rulers of the nearest city in unforgivable war crimes. Revelation of this information will topple the regime leading to a week of rioting followed by weekly coups as each new faction temporarily ascends to fill the power vacuum. There is a flat 1 in 6 chance per week that the current leading faction manages to solidify its control of the city to become the new permanent rulers.