From the publisher:
"Designed to work with the Advanced Player's Manual and other volumes in the Advanced Series, this book offers new tips, tricks, and options for GMs to improve their d20 games. With advice from the expert pen of Wheel of Time RPG and Bastards and Bloodlines author Owen K.C. Stephens, the AGMG provides insightful tools to take your campaigns in new directions, such as variant rules for critical hits, quick resolution mass combat rules, expert resources for building memorable villains and adventures, artifact construction and much more."