Dungeons & Dragons: A Young Adventurer's Guide - Beasts & Behemoths is all about creatures and potential adversaries you could encounter while adventuring, much like the earlier Monsters & Creatures and, to a lesser degree, Dungeons & Tombs, which features a Bestiary chapter. Having said that, the specific creatures covered in the different books appear to be carefully curated to ensure that each book brings something unique to the series and doesn't overlap with another book in the series - at least as of this writing. Even between Monsters & Creatures and Beasts & Behemoths, the selected content is divided between the books. For an example, both books have a section on Dragons, but the earlier Monsters & Creatures covered the Chromatic Dragons (White, Green, Black, Blue and Red, specifically), while Beasts & Behemoths covers Metallic Dragons (Brass, Bronze, Copper, Silver and Gold). [They're sort of, well, almost a growing encyclopedia, of sorts, covering various aspects of the Dungeons & Dragons role-playing realms, with each installment choosing some themed and curated collection of interests to feature.]
I don't know that Dungeons & Dragons: A Young Adventurer's Guide is necessarily one of those "gotta catch them all" sort of series, as different potential players might be more attracted to certain books in the series than others and the end goal would be to inspire enough interest that a player would invest in purchasing some rule books and actually playing and, as mentioned above, these books provide inspiring illustrations and descriptions, but not the rules needed to actually play a game. At the same time, however, these books could also be useful as hand-outs (well, either gifts or loan-outs, maybe) from DMs to players to provide them the knowledge that their player would have from being in the world, for those DMs who like to control how much information their players have about what they might encounter to avoid annoying disconnect between what a player might know and what their character would know. [Yes. That's it! Field guides. Well... After a fashion, anyway, I suppose.]
Beasts & Behemoths features thirty-five interesting races one might encounter on their adventures, divided into four categories: Tiny & Small, Medium, Large & Huge and Gargantuan. There are few entries in the extreme categories, with most of the beasties being around man-size up to the size of dragons. Each creature also features a Danger Level indicator, between 0 (harmless) and 5 (incredibly dangerous) [...well, that and "Epic", which is, well... Epic. Bring your friends. Bring your army. Bring your friend's army...] Additionally, each entry sports a couple of tips of things to do and things not to do if one should encounter the creature in question.
In addition to entries for each of these denizens, there are also four "Legendary" entries fleshing out specific legendary examples of some of the more interesting inhabitants. Additionally, there are five "Encounter" entries, which set the scene for an interesting encounter and possible choices that a player may face and consequences that could result based on what they choose. I found these entries to be well-selected and thought-provoking.
If you're interested in lycanthropes (werewolves and other were-creatures), then Beasts & Behemoths is going to be your favorite Young Adventurer's Guide. The Lycanthropes section (in the Medium chapter) has Werebears, wereboars, wererats, weretigers and werewolves. [Pretty much everything but were-houses can be found in this section.] Further, there is an Encounter entry for a Wererat, to get your imagination going.
As I mentioned in passing above, Dungeons & Dragons: A Young Adventurer's Guide - Beasts & Behemoths also has a section (under the Large & Huge chapter) for Metallic Dragons. For the uninitiated, Chromatic Dragons are the types of dragons that most people probably think of when they think of typical fantasy literature and movies. Evil dragons that burninate the hillsides and attack castles and such. By and large [very large], Metallic Dragons are Good, not Evil, and are sworn enemies of Chromatic Dragons, in fact. Within these pages, you'll find which Chromatic Dragon is the hated foe of which Metallic Dragon, as well as how they're similar and what their lairs are like.
Of the gambit covered in this volume, you will find monstrous natural races, such as Hobgoblins and Gnolls to the nigh-indestructible Trolls and cursed immortal Medusas. You'll find things that go bump in the Underdark, including Drow Elves and gargantuan Purple Worms. There are also Sphinxes, found in remote locales, guarding epic treasures and granting them only to those who prove themselves worthy. You can read about birds the size of dragons that perch in the highest of mountains - and (Pseudo)dragons the size of birds who can perch on your shoulder, should you prove yourself compatible, generous, a talented mage, and worthy of their companionship.
At a suggested retail price of $12.99 USD, the books in the Dungeons & Dragons: A Young Adventurer's Guide series aren't overly expensive, but again, collecting the whole (continuing?) series would cost more than the suggested retail price of a 5th Edition Player's Handbook, and, truthfully, you can get a Player's Handbook for around half price on Amazon as of my writing this, which is just a few dollars more than the suggested retail cost for two of these books. Still, they are inspiring and fascinating and I am glad to discover that Wizards & Spells was not, in fact, the last book in the series. I'm interested to see what they come up with next.
