The Dark Prognosticus is a book of prophecies that appeared in Super Paper Mario. The author of the book and the source of their knowledge is never revealed in the game. At the beginning of this powerful object is a warning: anyone who has possessed the book has never found happiness.
Over the years, many have fought over the Dark Prognosticus. Garson states during his story on the book that entire countries fell in a war over possession of the book, though the fall of these countries were already predicted in the book itself.
Another one of Garson's stories states that the very first Pixl, who came to be known as the Pixl Queen, was created by a magician using knowledge obtained from the Dark Prognosticus. After defeating the Pixl Queen, the being took the Dark Prognosticus to prevent a second Pixl uprising from occurring.
At one time, the Tribe of Ancients possessed the Dark Prognosticus. However, several of the tribe's members became possessed by the book's great power. They stole it, ran away, and hid the book. Officially having broken off from the Tribe of Ancients, these members became known as the Tribe of Darkness. The tribe guarded the book for centuries afterward, until Blumiere took it and became enchanted by the book's power, turning him into Count Bleck, the final owner. Bleck desires to use this book in hopes of "destroying all the worlds", the book apparently stating that the marriage of two beings that fit Bowser and Peach's description would create the Chaos Heart, which would open The Void to destroy the worlds. However, the book also speaks of a hero that would rise up and attempt to stop the destruction of existence. The Light Prognosticus was also written to counter this book, telling the prophecy from a more optimistic view.
Carson's story on Dimentio implies that Dimentio himself may have written the book; supporting this is that Count Bleck did not originally want Dimentio as his minion until he found the description of a similar being within the Dark Prognosticus. Something that also supports this is the fact that the Void is completely absent in Dimension D, a dimension created by Dimentio. The Dark Prognosticus also states Luigi (simply called the "man in green") is the perfect host for the Chaos Heart.
After the events of Super Paper Mario, the Dark Prognosticus "faded back into history."