The Book of Proliferation is said to have been dated before the fifteenth century. The Styx title means "from one comes many," referring to The Phase. According to Eddie, after The Phase of the fifteenth century was stopped, only a few of the books survived. Eddie smuggled one copy out of the Styx Citadel and brought it Topsoil with him to show Will and Drake the secrets of The Phase. This copy is currently in Eddie's possession.
The book contains details about The Phase, as well as a record of the last one. It has illustrations for how The Phase works and the transformation of the Styx women. It also contains information about the Armagi, the second stage of the Styx Warrior larva.
The book has a cover fashioned from human skin. It has a triangle on the front cover.