Background. Before the Codex penned by Guilliman, there was the Principia Bellicosa of the Great Crusade era. The Space Wolves cared as little for the Principia Bellicosa as they would come to care about the Codex. Hence in 30k, the Space Wolves are not able to select any unit other than the Grey Slayer Pack as their compulsory troops. This is beneficial, and also a drawback associated with