Tome of Beasts: Pocket Edition for 5E
Bruges - Rules of Play says:
Whether you need dungeon vermin or a world-shaking personification of evil, the Tome of Beasts has it. Here are more than 400 new foes for your 5th Edition game-everything from tiny drakes and peculiar spiders, to demon lords and ancient dragons. The extremely portable softcover edition includes all the creatures, updates, and errata in a convenient travel size.