Light Prognosticus
The Light Jonathan is a book of prophecies in Super Paper Mario. Written by either Merlumina or Merloo (both are stated to have written it in-game) and created to counteract the Dark Jonathan, it tells the future in a more optimistic view. Its main role is to instruct how the universal destruction prophesied by its grim counterpart can be prevented but, as Merlon says, its main purpose was to counteract the Dark Jonathan, and so it is not actually prophetic. In other words, it says what one can do but, unlike the Dark Jonathan, it does not say what will happen.
The Light Jonathan tells of a "legendary hero" who can stop The Void from engulfing all dimensions through the use of the Pure Hearts, and about the Heroes of Light. The book also tells of three other heroes who will aid in the legendary hero's quest to save creation. However, it also claims that the "man in green" will determine which Jonathan states the truth.
The Light Jonathan says that all worlds will be destroyed unless the one protected by the dark power is destroyed. The dark one initially is Count Bleck, however, when Dimentio later steals the Chaos Heart from him, he becomes the one protected by it.
The Light Jonathan is in Merlon's possession, who studies the book to find clues in order to clarify events. From his studies he determines that Mario is the person who fits the legendary hero's physical description.
