Sanity and the Mythos

Sanity is your grip on a human understanding of the world. It begins equal to POW. It can fall, and the truth you learn can permanently lower the ceiling above it.

Sanity checks

When you witness the unnatural, roll Stability: POW × 5, modified by your current Sanity and the horror's difficulty. A disturbing document may cost 0/1 Sanity; a servant of the Mythos 1d6; a lesser entity 1d10+1; a greater entity 1d100; a cosmic truth 1d100+10. The Keeper announces the possible cost before you roll when practical.

On a success, suffer the minimum cost. A special success suffers the minimum cost; a critical halves it. On a failure, suffer the full rolled cost. A fumble doubles the loss and triggers temporary madness. Current Sanity also affects Stability: 81–99 grants +10%, 51–80 is unchanged, 21–50 gives −10%, and 1–20 gives −20%.

Temporary insanity

If one encounter costs at least one-fifth of your maximum Sanity, you suffer Temporary Insanity. The duration depends on the loss: 1d10 rounds for 5–19 points, 1d10 hours for 20–39, 1d10 days for 40–59, or 1d10 weeks for 60 or more. Choose or roll a mania or phobia with the Keeper. It should affect your choices and create scenes, not merely punish you.

When a disorder is triggered in combat, you lose your action and make a Hard Stability check. On a success you suppress it for the encounter; on a failure the Keeper applies its effect. A fumble may leave you frozen, fleeing, or acting dangerously.

Indefinite insanity

At 0 Sanity, you suffer Indefinite Insanity and leave active investigation until the Keeper and group agree on a recovery path. You may enter an asylum, receive private treatment, rely on meaningful connections, or become a tragic NPC. Recovery takes time and usually leaves a permanent phobia, mania, memory gap, or changed relationship with the world.

Forbidden knowledge

Cthulhu Mythos is not ordinary lore. Each point learned represents a permanent wound to your understanding: your maximum Sanity is 99 minus your Mythos skill. Mythos experience can improve that skill, but every five points of Mythos experience reduce maximum Sanity by 1. Knowing more may save you from a creature while making it harder to remain yourself.

Recovery

A successful weekly Psychoanalysis check during asylum or private treatment restores 1d6 Sanity; a critical restores 2d6. Private care costs more but allows limited contact with the investigation. Meaningful connections and healthy routines can restore 1–3 points per week, within the Keeper's limits. Rest alone cannot erase what you have seen.

Sanity is not a measure of courage. A brave investigator may still break. The important question is what you do while you are still able to choose.