Behold. The Rule Book.
The Rule Book is a glossary of useful information. By right-clicking on a sigil or item, the rule book is brought up and flipped to the relevant page with a brief explanation of the sigil's or item's function. The rule book contains explanations of all sigils, items, and boons. The player may flip through the book by using the A and D keys.
Act I[]
In Act I, the rule book is placed to the left of the player in all battles once it has been accessed for the first time.
The explanations for the variable Power Stats of the three Tentacle creatures are partially obscured with ink.
The book contains the code to the safe (2-7-3) on the Mighty Leap sigil page. The Stoat instructs the player to find this code in order to free the Stinkbug.
Act II[]
This act does not contain a rule book. Instead, descriptions of each sigil can be read by hovering the cursor over a card bearing that sigil, although they do not state the name of the sigil, and the description for Kraken Waterborne is the same as regular Waterborne, to confuse the player.
Act III[]
In Act III, the rule book functions similarly to how it functions during Act I, the only differences being that it contains different sigils, no information on boons or variable Power stats (since neither exist in this Act) and has the appearance of a tablet to be more in line with Act III's technological aesthetic. When you finish a Build-a-Card event the rule book can no longer be accessed out of battles since it was placed on the conveyer belt and when Po3 sends the bot down the line, it pushes the rule book off the end of the conveyer belt.
Finale[]
Although these sections are relatively short, both Grimora's and Magnificus's sections contain unique rule books, each with a unique appearance. These include listings of various sigils seen in previous acts but not available during these sections, as well as various sigils that do not appear anywhere in the game and are included either to provide the illusion of these sections being fully fleshed out experiences that are inaccessible to the player (e.g. Blood Guzzler and Haunter), or are included as jokes to amuse players who find their entries (e.g. Apparition and Virtual Realist).