Statistics in Fighting Fantasy are quite simple: Skill and Stamina are the primary values. Also listed are the habitat they're typically found, the number encountered, Type (undead, humanoid, animal, other), Reaction (ranging from friendly to hostile) and Intelligence (high, average, low, none). All these are guidelines and the GM is encouraged to vary the statistics as needed.
What truly gives substance to the creatures are the descriptions of the creatures' various habits, abilities and tactics. When GMing a campaign, as opposed to playing a game book, the encounters need to be dynamic or they'll be a boring slugfest, and this book delivers on that need. Little creatures like Grannits (SK 4 ST 3) that one might easily crush in simple combat become menacing because their hides are indistinguishable (that word exactly) from the rocks in their environment and get a free first hit when they choose to attack. Imaging getting bit, falling back and landing in more that crawl all over you. Nip nip nip, the wizard panics and throws a fireball, blasting everyone. The goblin in the party dines on roasted Grannit.
The creatures are written for Fighting Fantasy: The Introductory Role Playing Game. As such, creature abilities are narrative (such as the aforementioned Grannit), involve tests of Luck or Skill by the Player Characters, or are an odds in 6 chance of succeeding. For example, Black Elves will hit with their bows 4/6 of the time, a test of Luck is required to dodge Gold Dragon breath, and a bite by a Cockatrice calls for a 2d6 roll on a table for the fate of the victim (Death, partial paralysis and skill loss, or nothing).
Not all the rules for different creatures can be readily plugged into your current FF or AFF campaign. For example, an Iron-Eater, a blob that drops from the ceiling and eats your metal armor, will causes a 1 Skill point loss for each item eaten. If you assume the players are equipped with armor from the beginning, then this diminished combat Skill may make sense. However if you don't have armor function as a boost to combat Skill, then you need to remember to rule a different consequence for the loss of a piece of armor.
This book is an excellent source of creatures for your FF or AFF campaign or to be adapted to use in any other game system. I recommend picking up a copy if you're a FF enthusiast or want a bestiary for your game system.