The Mrin Codex is a fictional book of prophecy mentioned many times in David Eddings' Belgariad and Mallorean series of fantasy novels. Together with the Darine Codex, it provides the principal instructions for the Child of Light and his companions during the Age of Prophecy. Unlike the Darine, the Mrin doesn't follow any chronological order, but instead jumps around in time. Belgarath discovers that the Darine can be used as a "map" to the Mrin, which expands on and confirms what the Darine says. The Prophecy confirms this with a humourously deprecating message to Belgarath in the Mrin.
The Prophecy which guides the Child of Light and his companions does not allow the sorcerers whose task is to glean their instructions from the Mrin, to understand what they are reading until the appropriate time. Belkira and Beltira are often given the task of interpreting the text, as their joined minds allow them to use the Darine in tandem with the Mrin more easily.
The part about the meeting of the Child of Light and the Child of Dark:
"Behold, it shall come to pass that in a certain moment, that which must be and that which must not be shall meet, in a meeting shall be decided all that has gone before and all that will come after. Then will the Child of Light and the Child of Dark face each other in the broken tomb, and the stars will shudder and grow dim"
In the Mirn Codex Belgarions companions are named:
Barak: The Dreadful Bear
Durnik: The Man With Two Lives
Hettar: The Horse Lord
Silk or Prince Kheldar: The Guide
Relg: The Blind Man
Lelldorin: The Archer
Mandorallen: The Knight Protector
Taiba: The Mother of the Race that Died
Ce'Nedra: The Queen of the World
Liselle: The Huntress
Sadi: The Man Who Is No Man
Zakath: The Empty One
Toth: The Silent Man
Poledra: The Woman Who Watches
The Mrin is composed of the assorted ravings of a madman who lived in the village of Braca, in the fens of Drasnia. The man had the mentality of an animal. He chose to live in a kennel, which he had to be chained to to prevent him running off. His hair was long and matted, and he spent his time wallowing in mud, making animalistic noises and rhythmically jerking on his chain. Belgarath notes that "there was no hint of intelligence or even humanity" in his eyes, until he starts prophesizing, at which point they become "alert and very penetrating". He could not speak any words before he was overcome by prophecy, so all he could speak was from the Prophecy, and this made the Mrin the most used source of Prophecy in the series.
The prophet's voice sounded almost exactly like the prophet of the Darine Codex, Bormik's. Belgarath confirms the authenticity of the Mrin prophets rantings as prophecy when the prophet mentions the Child of Light.