His Majesty the Worm is a new-school game with old-school sensibilities: a classic megadungeon experience given fresh life through a focus on the mundanities and small moments of daily life inside the dungeon. The Game Master is given tools to create a megadungeon called the Underworld. The players create adventurers to explore the Underworld in pursuit of their personal quests. Tarot cards are used as a randomizing element. Food, hunger, light, and inventory management are central to play and actually fun. Tarot cards are used to create an action-packed combat system that ensures that all players have interesting choices every minute of combat: no downtime!

The game has robust procedures. Characters adventure in the Underworld, rest in roleplaying-driven camping scenes, and plot long-term schemes in the City at the center of the Wide World. The relationships between companions, called Bonds, powers the rest and recovery mechanic of the game. Roleplaying drives the game forward. The book is 404 pages long, silver foil stamped and has a ribbon bookmark.