From the release:
The Adventures Dark and Deep™ Bestiary contains Over 900 monsters in one book, including well over a hundred brand-new monsters, with tons of illustrations.
Need we say more?
The Adventures Dark and Deep™ Bestiary is the third core rulebook for the Adventures Dark and Deep™ game, an expansion and revision of the original 1st Edition rules that defined the role-playing hobby for a decade. Based on Gary Gygax's original plans for expanding the game, Adventures Dark and Deep™ gives you new character classes like the jester, savant, mystic, and mountebank; new spells; a new combat system; new monsters; rules for weather and natural hazards; new magic items, and tons more. And it's all compatible with most old-school games, so you can use it with all your old and new adventures, settings, and supplements.
If you liked 1st Edition, you'll love Adventures Dark and Deep™.