J. Benjamin’s Books of Knowledge is an intriguing supplement: a collection of magical books that adventurers can study and thereby gain various magical benefits. The author suggests using this supplement in a campaign where permanent magic items are rare; the books described tend to have lesser magical effects, and thus allow a hint of magical ability without overwhelming the campaign.
For instance, the book Art of Axe-Throwing requires three days to read and increases the reader’s normal range with thrown axes by five feet. Eyes of the Kobold allows the reader to reduce the damage they take from a trap by their Intelligence modifier, and False Impressions allows the reader to gain advantage on an attempt to forge documents.
Many of the effects are trivial or extremely specific. Take, for instance, Flumph Grammar, a book that grants you advantage on Charisma (Persuasion) checks you make against flumphs! Is this a problem? Not exactly. I delight in the flavour these books give the world. The trouble comes when too many of these effects are gained by a player. Remembering conditional bonuses is hard, especially when they come up rarely. It’s a major problem I have with the Pathfinder feat system, which delights in conditional bonuses.
However, when I come across Secrets of a Repentant Thief, which grants the reader an understanding of some of the markings used by thieves to warn of danger, good targets or other matters, then I’m enchanted again.
The book has a few flaws when it comes to the correct expression of the rules. “You may add your proficiency bonus to Insight checks” is a bit problematic. Do you get this bonus if you are already proficient in Insight? And surely it should be to Wisdom (Insight) checks? There are also more than a few missing apostrophes, and the phrasing is tortuous at times. Consider: “You may add your proficiency bonus to all Deception checks you make against humanoid creatures you are actively engaged in reading their fortunes to, and doing so at their request. Additionally, while you are actively reading a humanoid creatures fortune at their request, whenever you make a Deception check against that creature, you may make an Insight check and use that result instead.”
Instead of using the regular attunement rules, several of the books use “minor attunement”, a parallel system that works in the same manner, except you may have three minor attunement items in addition to your three major attunement items. Given the minor effects of most of these books, this is not a bad way of balancing things. I would have preferred to see this limit applied to all the books, just to limit the number of strange effects in play.
Overall, whilst I’m not certain of the game implications of this supplement, I greatly appreciate the inspiration it gives for using minor magic treasures in my game.