Really useful supplement book for DMing. It's full of practical info that's great to have during a game, like combat information, DCs - all those fiddly bits of info that are scattered throughout the big rulebooks. Plus there's a ton of random tables that really speed up the game when a player does something unexpected. And the lairs! Honestly, if you don't have this book on-hand every time you DM, you're making life harder for yourself.
[5 of 5 Stars!]