From the introduction: Although a passenger has no abilities of its own, it grants its vessel (see the vessel section of Paranormal Adventures) a number of abilities based upon its vessel’s level while the vessel possesses an adequate amount of grace. When a vessel gains his first point of grace from his passenger, he must decide its subtype. The passenger’s subtype determines the benefits that the vessel gains from his grace overfloweth ability, as well as its overall personality and theme. Once the choice of subtype is made, it cannot be changed.