A solo+ survival mystery TTRPG utilizing step-down dice and card draw mechanics, Substratum Protocol is playable as both a solo game or guided by a GM.

When the anomaly appeared at the Earth's core, the Substratum Protocol was initiated. You are the best and brightest scientists we have left, our last hope to stem the apocalypse.  

You are the Substratum Expedition Team.  

With players taking on the role of Earth's best remaining scientists, Substratum Protocol is our entry into the Deep Delving Mystery genre (like Subnautica and In Other Waters). 

On their grueling journey to the center of the Earth, members of the Substratum Expedition will overcome challenges, gain clues and knowledge of the anomaly, discover creatures, aliens, cosmic horrors, and ultimately assemble their final hypothesis to overcome the apocalypse looming before them. 

The game intertwines hard science fiction with the inescapable, unknowable horrors of an anomaly tearing apart reality.

• Purpose-built for solo and multiplayer mysteries
• Unique dice and card draw resolution mechanics
• Take special Actions whose outcomes can chain together
• Collect beaten cards during Skill Checks to power your suit's abilities
• A self-contained story, with unlimited possibilities and outcomes
• Quickly build unique and interesting characters at the table
• 36 unique clues to discover, 36 questions to answer
• 10 sectors to explore, each one stranger than the last
• 120 events and encounters to surprise and stump your players
• Build the Last Hypothesis: When they have learned all they can, the scientists must pour over their knowledge of the anomaly, construct the Last Hypothesis and enact their plan. Will it be enough?

A fantastic team brought Substratum Protocol to life, including the group behind the wildly popular dwarves in space TTRPG, Stoneburner by Fari RPGs!

• Illustrations by Galen Pejeau
• Editing by Eric Lazure
• Developmental Editing by René-Pier Deshaies-Gélinas
• Layout Direction from Tony Tran
• Writing and Design by Andrew Boyd

	The Hints and Hijinx system that powers Substratum Protocol began its life as a purpose-built solo mystery TTRPGs system, with over twenty games made with it. This is why we call Substratum Protocol a "Solo+" game - we started with a solo system, and built it into a robust multiplayer game.

Substratum Protocol supports two styles of solo play - a more complex, free form method similar to playing multiplayer, and the original Hints and Hijinx format of solo play that is quicker to pick up and play through an expedition. Both are a ton of fun and give you room to explore and discover new mysteries on each play through. All the members in your team, creatures you meet, dice rolls, adventures, clues, setbacks and successes of your expedition can be captured in a book to look back on or share.