From the introduction: Just like Monster Manual Expanded, this aims to provide Dungeon Masters more options and flexibility in designing adventures and dressing up their dungeons with a wider variety of creatures and characters that are based on the Monster Manual, Volo's Guide to Monsters, Mordenkainen's Tome of Foes, and many others. Finally, it also adds variants that provide a nostalgic and classic feel that DMs experienced with the older editions are probably familiar with. In total, there are over 380 creature stat blocks in this book at the Dungeon Master's disposal!