Fatal Fortress Game Master's Tome, 6th Ed.

Fatal Fortress Game Master's Tome, 6th Ed. is a book in Prey (2017) and Prey: Mooncrash.

Transcript
[Excerpt from the 6th edition Fatal Fortress Rule Book]

Greetings, Game Master!

Fatal Fortress is a world deprived of sunlight. As Game Master, you will guide a troop of stalwart adventurers through glittering caves crawling with Ratmen, into battles against horrors that have slept for centuries, and deep into the secret heart of the Fatal Fortress itself.

Unlike other games, Fatal Fortress has no set character classes, instead encouraging players to play their own way by mixing and matching abilities as they are faced with new challenges. This game also features a dramatic magic system where players create their own spells by drawing and combining runes.

Each player will need a character record sheet, a miniature to represent their character on the combat map, a full set of polyhedral dice, and a thirst for danger!

Location
In Mooncrash, the book is found in habitation modules 1-8.