Classic-Style Sanity rules for GURPS, Part 1

These rules add Sanity rules similar to those found in Call of Cthulhu to GURPS.

To those not familiar with these rules, I will first give an explanation of the basic concept: When characters encounter horrible things in the world, their sanity is tested. Often, they will become less sane, which makes them less able to resist future tests of their sanity, creating a death spiral leading to inevitable insanity.

The way this is achieved in classic Call of Cthulhu is by having a Sanity score that one attempts to roll under with a d100. If you fail, you become less sane, your sanity score is lowered, and then you are more likely to fail further sanity checks. In addition, the loss of sanity is accompanied by a variety of sorts of madness in the form of phobias and manias. That's it.

In this post, I will attempt to recreate these rules as nearly as I can for use in GURPS. In a future post, I will attempt my own version which will improve on these rules in certain ways (using 3d6 rather than the d100, and adding difficulty modifiers to the roll, so that it is not the same difficulty to resist seeing a rat gnawing on a body as it is to resist staring into something which man cannot comprehend, and also by having lost sanity impose a penalty on the 3d6 roll rather than rolling directly against the sanity score itself).

Core Concepts

 

Madness Tables from GURPS Horror 

Rather than figure out how to represent the various effects of madness mechanically in the game, I will be using the madness tables found on pages 143 and 144 in the fourth edition of GURPS Horror.

d100
We're using these for now to exactly emulate the original rules.

New attribute: Sanity

Sanity begins at 50, goes from 1 to 99 (with the maximum possible score reduced by their Mythos Knowledge), and may be bought up or down as normal, at a cost of 2 character points for each 5 Sanity Points.

New skill: Hidden Lore (Mythos Knowledge)

This skill increases rapidly during play as the characters probe things man was not meant to know. A character's knowledge of the mythos reduces their maximum Sanity. Each character point a character has in Mythos Knowledge reduces their maximum Sanity by four points. For instance, Mythos Knowledge at a level of IQ+5 costs 20 character points, and thus reduces their maximum sanity by eighty points, from 99 to 19.

Sanity loss caused by mythos entities increases a character's Mythos Knowledge skill. If a character has no points in the skill, then their first encounter with a mythos entity gives them a point in the skill. Each encounter with a mythos entity beyond this gives a chance to increase skill. Make a sanity check. On a failed roll, the character gains one character point in Mythos Knowledge.

The primary source of Mythos Knowledge in the world are tomes such as the Necronomicon. Reading these gives points in the Mythos Knowledge skill. These range from 1 to 4 points. Reading such tomes risks sanity loss as normal, of course.

Sanity Check

A sanity check is a roll of 1d100 against the character's current Sanity score. If the character rolls under their Sanity score, they succeed.

Sanity Loss

Horrific situations, encountering entities from beyond this world, learning unsettling truths about the nature of reality, etc. can all cause a character to lose sanity. Potential sanity loss is indicated by two numbers. The first number is the amount of sanity lost if the character succeeds on their sanity check. The second number is the amount lost if the character fails their sanity check.

Mental Break Threshold

Characters have a mental break threshold equal to their current sanity divided by 10 (rounded down).

Effects of Sanity Loss

 

Mental Break

Whenever a character suffers sufficient sanity loss from a single source to reach their mental break threshold (Their current Sanity divided by 10), they risk suffering a mental break. The GM chooses an appropriate skill related to the source of the lost sanity, usually Hidden Lore (Mythos Knowledge) and the character must roll against that skill (If Hidden Lore is chosen, but not possessed by the character, it may be made at a default of IQ-5). This is to test the character's understanding of what they have witnessed.

If the character fails the skill roll, then their comprehension was not sufficient to send them into a bout of temporary insanity. They come up with some plausible explanation or comforting lie. Whatever the case, they are able to carry on.

If, however, they succeed on the skill roll, they have grasped some truth about the nature of reality which their mind cannot reconcile with their understanding of the world. Ghosts are real, aliens walk among us, Nickelback won a Grammy. Whatever they have learned shatters their mind temporarily. They suffer from a bout of temporary insanity, represented by a roll on the Short-Term Conditions table.

Temporary Insanity begins with a bout of madness. Get out your copy of the most excellent fourth edition of GURPS Horror by Kenneth Hite, and roll on the Madness Table of your choice for a short-term condition. These are found on pages 143 and 144.

Also roll a d6. On a roll of 6, the character gains a Long-Term Condition. The GM may either roll on the table or choose from the list of Conditions on page 144 of Horror.

After the short-term condition has ended, the character continues to suffer from their temporary insanity for the next 1d10 hours.

During this time, the character suffers from delusions and hallucinations. Is that the harmless wail of a banshee as it approaches, or have Nickelback begun to practice nearby? You can't be certain...

If a player wishes to question one of these delusions or hallucinations, they may do so by making a reality check.

A reality check is simply another sanity check. If the player succeeds, they have seen past their delusion or hallucination and returned to normal... whatever that is for them now that they have glimpsed some fragment of the truth.

If they fail, then the delusion or hallucination continues, and for their effort the character suffers an additional point of damage to their Sanity, and suffer another temporary bout of madness (back to the short-term conditions table), and the delusion or hallucination intensifies.

Continuing Insanity

If a character loses more than a fifth of their total Sanity in a single day, they become insane until they are able to rest in a safe place for an extended period. The GM represents this as they see fit, perhaps by rolling on the Medium-Term Conditions table. The character should certainly be "out of commission" as it were while in this state. The player should roleplay this appropriately.

Permanent Insanity

When a character's Sanity reaches zero, their mind, essentially, is no more. Some physical semblance of what they once were might remain, but this is no more than a vessel containing shattered remains. A merciful GM might allow a recovery of a sort, perhaps enough to leave a mental institution to wander aimlessly for the rest of their days, but such is not at all to be expected.

Repeat Exposure

Characters become numb to horrors after experiencing them multiple times. The first time a character reads the terrible truths contained within the Necronomicon, their mind might shatter. Yet it does not shatter further with each subsequent read.

Once a character has taken the maximum result in sanity loss for exposure to a particular horror, they no longer suffer sanity loss from that horror. For instance, if the maximum sanity loss from seeing a shoggoth is 20, a character cannot take more than 20 sanity loss from that source. Beyond that point, additional exposure causes no more sanity loss.

Restoring Sanity

 

Merciful GMs may allow characters to restore some of their missing Sanity at the end of each session, or each campaign. 1d6 points might be restored.

This is only for the merciful, however. The less forgiving GM might require the characters to undergo extensive psychological treatment to be so restored--or deny its possibility outright!

After all, that which has been seen cannot be unseen...

Examples of Sanity Loss

0/1d-2  Encounter a mutilated animal carcass
0/1d-1  Encounter a human corpse
0/1d-1  Encounter a stream which flows with blood
1/1d    Encounter mutilated human corpse
0/1d    Awake trapped inside a coffin
0/1d    Witness friend's murder
1/1d    Encounter someone you know to be dead
0/1d+2  Endure torture
1/1d+2  Watch a corpse crawl from its grave
2/2d+5  See a giant disembodied head fall from the heavens 

Sample Monsters 

Ghoul: 0/1d6
Shoggoth: 1d6/1d20
Great Cthulhu: 1d10/1d100