An empty book made of dark leather gilded with gold inlay. The cover seems to shift in hue and saturation. Every time you defeat an enemy make a persuasion, insight, history, nature, investigation, or survival check to learn about the defeated creature. The knowledge learned depends on the outcome below and is permanently stored in the compendium. There are five possible outcomes.

DC 5 + the creatures CR: You learn the basics of the creature; what it's called and the type of creature it is (undead, beast, etc.).

DC 10 + the creatures CR: You learn the the above as well as become familiar with the creatures attacks.

DC 15 + the creatures CR: you learn all of the above as well as the creatures strengths, resistances and immunities. As well as any lore surrounding the creature.

DC 20 + the creatures CR: you learn all of the above as well as the creatures weaknesses including its worst attribute (ability save), as well as any spells it knows or abilities it has

DC 25 + the creatures CR: you learn everything there is to know about the creature

Using this book is an action if used in combat