2–9
Move. Climb. Endure.
The normal, undamaged range for a balanced investigator. Stamina damage removes successful totals from the bottom, beginning at 2.
An original horror-investigation RPG
A Mythos Investigation
Follow the evidence.
Face what it leads to.
A lightweight roleplaying system for tabletop investigations and solo gamebook adventures. Explore unsettling places, uncover forbidden knowledge and survive the consequences.

01 / A trail into the unknown
A locked room. A missing witness. A discovery that makes the evidence harder to explain.
These are the kinds of mysteries this system is built to support. Your investigator brings practical abilities, knowledge and equipment. What you examine—and what you risk to examine it—drives the adventure.
The rules distinguish between physical action and mental effort. Injury makes physical tasks harder. Psychological strain narrows the chances of succeeding at mental tasks. Survival and understanding pull against the damage an investigation can leave behind.
The horror lives in what you uncover. The rules keep the immediate task clear.
02 / The core system
Add two ten-sided dice. For physical actions, low totals are better. For mental actions, high totals are better.
2–9
The normal, undamaged range for a balanced investigator. Stamina damage removes successful totals from the bottom, beginning at 2.
11–20
The normal, undamaged range for a balanced investigator. Sanity damage removes successful totals from the top, beginning at 20.
For a balanced investigator, a total of 10 succeeds at neither type of test. A physical or mental inclination extends the corresponding range to include 10.
| Difficulty | Physical | Mental |
|---|---|---|
| Easy | Roll 3d10 · keep lowest two | Roll 3d10 · keep highest two |
| Normal | Roll 2d10 · add both | Roll 2d10 · add both |
| Hard | Roll 3d10 · keep highest two | Roll 3d10 · keep lowest two |
Examine the principle
Adjust the damage to see which totals can still succeed. See how Stamina and Sanity damage narrow the successful totals.
Physical success 2–9
Mental success 11–20
03 / The visual world
An unexamined doorway. An interrupted line of research. A witness who keeps looking. The answers remain unseen.


04 / The case file
Built for stories of investigation, risk and discovery.
Download Core Rules v0.3 Download Character Sheet v1.2An independent homebrew system by Whit3star. Not an official Call of Cthulhu product.