Call of Cthulhu d100
While vicious monsters and crazed cultists are quite threatening to your physical health, they can be just as threatening to your mental health. Finding the truth behind the mysteries of the Cthulhu Mythos will take a toll on your character’s psyche, and though skill and luck may enable your character to keep their mind intact, going insane is a real possibility.
Any time your character encounters the terror of the Cthulhu Mythos, or sees something mundane yet horrific, such as the mutilated corpse of a dear friend, you need to make a percentile roll against their current SAN. If you fail the check, your character will lose a certain amount of SAN. if you pass the check, they will lose less SAN, perhaps even none at all. The amount of SAN at risk is usually described with two numbers separated by a slash, such as 0/1D6 or 2/1D10. The first number is how much SAN your character will lose if you succeed with the check; the second number is how much they lose if you fail the check.
Regaining your sanity is possible, but typically difficult. You may get a few points of SAN returned after a successful scenario, or as a reward when you raise one of your character’s skill ratings above 90%, but other methods of regaining SAN such as therapy may be a long and troublesome process.
Losing sanity has an affect on your character. There are three different penalties that can be applied as a result of losing your mind: temporary insanity, indefinite insanity, and permanent insanity.
Temporary Insanity: If a character loses five or more points of sanity at one time, then they have experienced an event so traumatic that the character may begin suffering from temporary insanity. The host will ask for a percentile roll against five times the value of the character’s Idea attribute. This is a roll that you actually want to fail. If you succeed on the check, then that means your character fully understands the implications of what they have seen, and temporarily goes insane as a result. When a character goes temporarily insane, they may (at the host’s discretion) faint, scream wildly, or even flee in terror. The effects of temporary insanity will last for 1D10+4 rounds. Afterward, the character may still be left with a mild phobia or PTSD.
Indefinite Insanity: If a character loses a fifth or more of their Sanity in one hour of in-game time, they will suffer from indefinite insanity. Such bouts of insanity last, on average, 1D6 months of game time. The character may have to deal with continuous symptoms of their insanity, such as amnesia or depression. Other times, the symptoms may be sporadic, and only manifest at random moments. For example: multiple personality disorder or intermittent explosive personality. Often, the result is an anxiety disorder of some sort, perhaps causing the character to suffer from flashbacks and recurring nightmares.
Permanent Insanity: If a character loses ALL of their Sanity, they go permanently insane. This may not actually be lifelong insanity, but it will certainly be at least a year’s worth of game-time before the character recovers from the trauma they experienced. A character going permanently insane will have to be committed to an asylum. A lucky character may have a hope to one day be released, but this is likely the end of the character’s run as a player’s investigator.