This 64-page softcover book is a supplement for the 1st edition of the Pathfinder roleplaying game from Paizo Publishing. Pathfinder is based on the 3rd edition Dungeons and Dragons rules, which use the d20 ruleset. This book takes an expanded look at some of the classic dungeon monsters, including bulettes, gelatinous cubes, owlbears, purple worms, and rust monsters.