Book of Beasts: Underdark Vault

From publisher blurb: This edition of the Book of Beasts centers on a number of creatures that come from the Underdark or could easily be encountered there. Each of these monsters was chosen because it can easily be dropped into adventures in the Underdark, be used as an interesting one-off encounter, or employed by NPCs (or other monsters) as a guardian. They should be particularly useful to DMs running Out of the Abyss.