The Chronicle of Vun the Damnéd is a leather-bound journal detailing the adventures and researches of the apostate magus, Vun the Damnéd. Vun the Damnéd was a wizard who pacted with foul things and took up the path of the warlock after a chance meeting with the infamous Gingor the Seeker. He merrily pacted with multiple entities across the planes, dabbling in demonology, infernalism, necromancy, and the foul lore of the Far Realm. (Although not mentioned in the book, this activity likely has something to do with his mysterious disappearance.) When you consult the Chronicle on forbidden arcana, take +1 forward to your next spout lore check on an appropriate subject.
In addition, the book also contains the complete litany necessary to enact the Liquescent Aspect of the Weird God, as well as the location of the Weird God’s secret fane on Khaldun.
(Parties interested in further information on the Weird God are directed to pages 59 and 109 of Carcosa by Geoffrey McKinney. Naturally, if you wish to include the Weird God in your own campaign setting, this book will tell you where his secret fane is located.)