Cthulhu-like Sanity Rules for Shoreline GURPS Collective

Gene Michael Stover

created Sunday, 2022 April 16 (version 0, strawman)
updated ???

This is https://cybertiggyr.com/sanity.html

What's this?

The third adventure from the Children of Lovecraft Country adventures relies on sanity so much that we need some sanity rules that resemble the sanity rules for the Call of Cthulhu rules.

The Call of Cthulhu rules tend to create a quickening spiral down into insanity if a character fails several checks in a short span of time. It would be nice to duplicate that.

Let's start with Roger Bell_West's Sanity for GURPS rules as suggested by Dustin, but I'm adding some clarifications.


  1. Let's create a Fearfulness counter. It starts at 0 for most characters. You want it to be low. (If some really excellent things happen to you, it might go negative.)
  2. A fright check is now modified by your Fearfulness. (See the Fright Checks section for details.)
  3. We could talk about Sanity as [IQ - Fearfulness], but we don't need to track it on the character sheet.
  4. If Sanity is ever 2 or less, the character is insane & unplayable.

Fright Checks

There are two kinds of fright checks: Normal & Cosmic.

For a Normal fright check, do this...

At the GM's discretion, we might be looking at a Cosmic horror fright check.

Decreasing Sanity

In the Call of Cthulhu rules, when you lose a fright check, you make another die role to see how it affects your sanity. (It usually lowers it.)

For example, in CoC, they might say that a character who loses a particular fright check loses “0/1d3 sanity points.”. That means that, if you failed by a small amount, it doesn't change your sanity, but if you fail by a lot, you roll 1d3 & lose that many sanity points. Sometimes the loss is temporary (like for the adventure), but sometimes it's permanent.

When you fail a fright check by 4 or more, let's increase Fearfulness by [amount_you_fail - 3]. So if you fail by 4, you increase Fearfulness by 1. Here's a table...

roll - fright_check_targetchange to fearfulness
≤ 0made it!

The idea is that changing your fearfulness by failing a fright check is rare, but as it occurs, the bell curve on those 3d6 die rolls makes it more likely & bigger, sort of like in the CoC rules.

Normal horror vs Cosmic horror

Normal horror is mostly about the mental shock from witnessing immediate physical dangers, though some other things fall into normal horror. Cosmic horror is about humanity's place in the universe.

Examples of normal horror are...

Examples of cosmic horror include...

An example of a special situation would be seeing an army of dead rise from their graves. It's cosmic because you're seeing the dead rise, but at the same time, it's normal horror because it's a hostile, overwhelming force. So make both horror checks. Right now! 8-)

Cthulhu Mythos Knowledge

It's not the same as regular occult knowledge or forbidden. It's a specific skill.

Cthulhu Mythos knowledge is dangerous! That's why it affects cosmic horror fright checks.

Recoverying Sanity

Recovering sanity is the same as reducing Fearfulness.

You lower Fearfulness by 1 point every 6 months that you have no adventures & no personal hardships. In other words, if you live a boring life for 6 months, you lower Fearfulness by 1 point (but never below 0).

If you spend 1 character point, devoce an in-world month to it, and have an in-game explanation such as psychotherapy, meditation (with a guru helping you), or a vacation (with no adventuring!), you lower fearfulness by 1 point (but never going negative). (This is what's suggested in Roger Bell_West's Sanity for GURPS.)

You can buy Fearlessness or Unfazeable with character points as normal.

Change Log