Dungeons & Dragons 3rd Edition was released in 2000. The first book containing monsters, one of the essential elements of the game, to be published was the Monster Manual, released along with the other two "core" rulebooks. Wizards of the Coast officially discontinued the 3rd Edition line upon the release of a revision, known as version 3.5, in 2003, with the Monster Manual reprinted for the revised edition. In this edition, killing monsters as to gain experience points was complemented by other achievements like negotiating, sneaking by or investigation. Additionally, the concept of challenge rating of monsters was introduced, a number to gauge their danger compared to the player characters' level. Further new elements were the grouping of creatures into defined types, and templates, which were not monsters in themselves but a set of changes that could be applied to a creature or character, like celestial versions of animals or vampires. Reviewer stylo considered this an "interesting new approach". The depictions of monsters were considered much improved as compared to earlier editions, with the exception of the Planescape setting. Animal studies scholar Matthew Chrulew observed that "the ideological work" of implementing creatures in the game "is performed by text and image in tandem" which "both conform to a logic of consumption and control. The images are certainly supplementary to classification, but hardly disturbing of it."