The Bestiary contains a list of all species found in the four realms. These species are divided into five distinct categories:
While the narrator is free to modify any template as desired for a particular NPC, a common way to do this is to add differentia. The differentia section includes a suite of modifications that can be applied to any template; each will also suggest how much the challenge rating of the NPC increases by adding the differentia.
Some templates have a few to begin with - their challenge rating has already been adjusted accordingly.