2018 · 资料书（用于增强玩法的规则/选项）
Operation Unfathomable Players' Guide
A player-facing guide to the Underworld setting, featuring comics, background information, rumors, and a partial map to help prepare for the initial scenario. It adds two playable species, two character classes, new spells, unusual items, and a custom character sheet. The spells and items duplicate those found in the main adventure module.
技能型（购买或获得技能）基于属性/数值（STR、CON、PER 等）等级制（获得经验值并升级）
免费，支持网页、Android 和 iOS
用 Ludoya 玩 Operation Unfathomable Players' Guide
游戏信息（人数、游戏时长、年龄、制作人员）来自 BoardGameGeek。