2018 · 소스북(플레이 향상용 규칙/옵션)

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.