Sanity and the Mythos

Sanity is your grip on a human understanding of the world. It begins at POW, capped by Maximum Sanity, and falls when the truth becomes impossible to deny.

Stability checks

When you witness the unnatural, roll Stability against POW × 5, modified by current Sanity and the horror's difficulty. Current Sanity modifies the target: 81–99 grants +10%, 51–80 is unchanged, 21–50 gives −10%, and 1–20 gives −20%. Use the normal percentile ladder: 01 is Critical, one-fifth is Extreme, one-half is Hard, and the full target is Regular. Fumbles are 96–100 below effective 50 and only 100 at 50 or higher.

A Sanity event is written X/Y: success loses X and failure loses Y. A Critical may halve the success loss. A fumble doubles the loss and triggers a bout of madness when appropriate.

Madness

A loss of 5 or more Sanity in one scene, or a fumble, causes a bout of madness. Lose the next action and choose a response such as fleeing, freezing, hiding, lashing out, dissociating, or seeking reassurance; it lasts 1d10 rounds unless the scene ends sooner. Losing one-fifth or more of Maximum Sanity in one encounter also assigns a temporary mania or phobia. Its duration is 1d10 rounds for 5–19 lost, 1d10 hours for 20–39, 1d10 days for 40–59, or 1d10 weeks for 60+.

At 0 current Sanity, suffer Indefinite Insanity and leave ordinary investigation until the group agrees on a recovery path. Treatment, meaningful connections, and time can support a return to play.

Forbidden knowledge

Maximum Sanity is 99 − Cthulhu Mythos. Each point of Mythos knowledge reduces that maximum by 1. Mythos experience may improve the skill, but learning more makes recovery harder.

Recovery

Structured Psychoanalysis can restore 1d6 Sanity per week on a successful check; a Critical restores 2d6. Meaningful connections and healthy routines may restore 1–3 per week within the Keeper's limits. Recovery never exceeds Maximum Sanity and cannot erase what the investigator has learned.