Sunday 16 September 2018

Trail of Cthulhu houserule - merging Stability and Sanity

The Trail of Cthulhu sanity rules are driving me mad. Two interacting abilities, rules spread out over multiple sections - I suspect this is intentional, to give you a taste of what the characters will be going through. Much as I love Kenneth Hite's take on Call of Cthulhu, here is a house rule (with inspiration from here) to merge Sanity and Stability. For ease of use, this is also a summary of existing Sanity rules in Trail.

I'd love feedback on this! 

Read the entire thing below or in google doc


After five read-throughs, I think I finally understand what Trail is trying to do with its Stability / Sanity system. Their rules let you keep your resistance to acute stress (and spellcasting ability) while gradually impairing your overall mental health, but it just has too many moving parts and subdivisions for me.

My design goals for this house rule:
  • simplify and speed up the mental health system by merging Stability and Sanity into one stat 
  • enable the downward spiral where lower Sanity -> lower resistance to Sanity damage 
  • make Mythos Lore a more attractive skill to raise and have 
  • keep low-Sanity spellcasters viable

The level of detail I'm willing to sacrifice:
  • characters that have ultra low Sanity but are still very composed (high Stability)
  • two types of mental stress damage to deal out 


(Not "if". Trail of Cthulhu is about doing what needs to be done while you ride the downward spiral.)

The Sanity stat tracks how close your mind is to breaking from all the awful things you'll be exposing it to. Like health, but for your piece of mind. Knowledge and encounters with the Mythos are especially damaging: this is the catch-all term for all the evil, supernatural and alien things making scary noises behind the curtain of "real life".

Sanity mechanic example. After repeated shocks, this character’s Maximum Sanity has dropped to 10 from 12. Their Sanity rating was lower than that, so no worries yet. They still have 8 Sanity points they can use until they become shaken, blasted, or permanently insane.
Munch's The Scream from here.


Trail of Cthulhu uses separate Stability and Sanity skills. This house rule merges and calls the result Sanity because I like asking for a Sanity Check during play. Apply only Stability losses (for instance from spells) from the Trail book; ignore its Sanity losses.

Sanity rating is your overall resistance to encounters with the weird, the scary and the vile.
  • Sanity rating starts at 4; you can increase it using build points during character generation or during the game up to your Maximum Sanity. 
  •  For every 3 Sanity rating, you get to pick a Pillar of Sanity that helps you recover Sanity points during the game. If these Pillars are threatened or destroyed, you stand to lose Sanity. 
  • Sanity rating goes down when a horrible encounter (Mythos-related or 5+ points loss on the tables below) drops you to negative Sanity points, or rarely when your Maximum Sanity forces it down.
  • At Sanity rating 0, you are incurably insane. Game over. Either head for the asylum or learn to love the horrors of the Mythos and become an NPC cultist.

Sanity points are eroded by real world stuff like violence or torture or by seeing the supernatural in action.
  • You start with Sanity points equal to your Sanity rating. Like health points, Sanity points can go up and down quickly during a session.
  • You get penalties to function and may get a delusion or madness condition when you drop below 0 Sanity points.
  • At -12 Sanity points, your mind breaks permanently. Game over.
  • Going against your character's Drive (core motivation) will cost you 4 or 2 Sanity points, but following your Drive gets you back 2 or 1 Sanity points. The exact amount depends on how much you would be going against type to resist an action.
  • Sanity points can also be recovered by spending time with a Pillar of Sanity (see below), via the Psychotherapy skill, or between adventures.
  • Denial or fainting can mitigate Sanity losses - see below.

Maximum Sanity is how high your Sanity rating can ever be.
  • Maximum Sanity drops when you learn the truth about universe and humanity's place in it, represented by gaining points in the skill Mythos Lore.
  • Maximum Sanity starts at 12 and can only go down.

Mythos Lore - this academic ability is used to gather or intuit knowledge about the Mythos, and to partly power magic spells. 
  • Use Mythos Lore to get a hunch or, with a point spend*, a clear hint about the Mythos horrors behind your current predicament. This risks blasting your Sanity points with a dark revelation. See the table below.
  • Mythos Lore cannot be bought with build points, only from forbidden tomes or horrible experience.
  • You can use 1 Mythos Lore point to pay for 1 Sanity point as part of casting a spell, but you always have to pay one Sanity point. This counts as a Mythos encounter if you drop below 0 Sanity points.
  • If you lost Sanity rating after being Shaken or Blasted, you can choose to gain an equal number of Mythos Lore points. This will lower your Maximum Sanity but not lower than your newly adjusted Sanity rating.
* this links to how Trail lets you gather clues; just having a skill is enough to get basic clues, spending points gets you extra useful options.


Compared to the Trail of Cthulhu book, Mythos Lore just got an upgrade. By the book, you can gain it by reading moldy old tomes - now, getting jumped by a Shoggoth is also an option. This lets you recoup a bit of your Sanity damage as a dubious ability. But don't be afraid that players are getting coddled. Mythos Lore to puzzle meaning out of chaos will cost more Sanity, and even using it as extra magic points (inspired by Trail's Rough Magics supplement) still costs you some Sanity.


Tor esist losing Sanity points, roll a d6 when your character is at risk of Sanity loss - see the table below.
  • You can spend Sanity points to add to the roll. The difficulty for the roll is 4 for mundane world stuff, 5 for Mythos-related events. You cannot spend your Sanity under -11.
  • "A 3-point Sanity check" means you risk losing 3 Sanity points plus any Sanity you spent on the roll. Generally not worth it for low point losses, but interesting to resist big shocks.
  • When multiple shocks apply during a scene, only the worst one counts. (If you get a strong Déjà Vu (2 points) and are ambushed later in the same scene by a Ghoul (5 points), you lose only 3 extra points for a total of 5.)
  • Likewise, when a Mythos event first drops you to Shaken, then to Blasted, you only lose 2 Sanity rating total, not 1+2 = 3.


So you failed that Sanity check - great news! Time to roleplay acute distress. Here's what happens at different values of Sanity points:

>0        Controlled as always

-5       Shaken - cannot spend from investigative pools. General ability difficulties +1. If you were shaken by a Mythos event or a shock of 5+ points, lose 1 Sanity rating.

-11     Blasted - as Shaken, and gain a mental illness (p77 ToC). Actions are limited to panicked flight, frenzied attacks on any perceived threat, crazy babbling etc. Lose 1 Sanity rating, or 2 if you were shaken by a Mythos event or a shock of 5+ points.

-12     incurably insane. Can commit one last act of self-destructive heroics, then collapse.

If you lost Sanity rating during a Mythos encounter that left you Shaken or Blasted, you can choose to gain an equal number of Mythos Lore points. This will lower your Maximum Sanity, but not lower than your new, adjusted Sanity rating.


Maybe, like many sensible folk, you don't want to see your mind drain away. Here's your options.

  • Repeated exposure to a particular event lowers the difficulty: after [difficulty] exposures, the difficulty drops by 1. (Keep track of how often you get chased by Ghouls. At some point they grow on you. Then you'll really have something to worry about.) Exception: spellcasting.
  • Fainting - if you voluntarily faint for the rest of the scene, you lose only 1 Sanity point (except for losses such as using spells, your own spends and use of the Cthulhu Mythos skill).
  • Denial - if there is no hard proof of an event at the end of the investigation, reduce your total Sanity rating loss by 1. Make up an alternative explanation or memory and prepare to lose that point of Sanity rating if your fabrication ever fails. STICK TO YOUR STORY.

    (Pro tip: carry gasoline to make sure there's no physical evidence after your investigation. Extra pro tip: carry a tranquiliser for use on PCs with the Drive to catalogue, learn from or boast about their adventures, as they'll want to save any mementoes.)


To regain lost Sanity points:

  • recover 1-2 Sanity points when you follow your Drive into danger.
  • gain 1-2 Sanity at the end of an investigation, or more if you significantly hindered the Mythos.
  • recover Sanity points by undergoing Psychoanalysis (difficulty 4, 3 for Clergy of Alienists - recover 2 Sanity for every extra point of Psychoanalysis spent in addition to those added to the die roll.)
  • spend time with a Pillar of Sanity (see below).
To raise Sanity rating: spend build or experience points to raise it up to Maximum Sanity.

To raise Maximum Sanity: cannot be raised, only lost.


For every 3 points of Sanity rating, pick one of the following Pillars of Sanity. You can only have one moral stance and one place of safety. You can use each type of Source of Stability once per session to regain some Sanity. If you lose 3+ Sanity rating, decide which of these Pillars of Sanity no longer holds any meaning to you. If you have no Pillars of Sanity remaining, all your Sanity checks are at +1 difficulty. If a Pillar of Sanity is lost, destroyed or invalidated, lose 1 Sanity rating and 3 Sanity points.
  • Moral stance - A core belief: religion, family honor, human dignity, scientific progress, laws of physics, beauty of nature, goodness of mankind, aesthetics and art, patriotism, love for home town. Contemplate your moral stance for a few minutes in a place of safety and calm to regain 1 Sanity point.
  • Treasured symbol - Your country's flag, a family photograph, a gift locket. Contemplate your treasured symbol for a few minutes in a place of safety and calm to regain 1 Sanity point.
  • Person of solace - A living person dear to you: a best friend, close colleague, family member. Interact with your person of solace in a safe place for 6 hours to regain 2 Sanity points.
  • Place of safety - A hide-out or parents' house, the site you first fell in love. If you can spend at least 24 hours in your place of safety without being under threat or drawing danger to it, you regain 3 Sanity points.


Same info as in the Trail rulebook, but reorganised for ease of reference during play.

Physical danger
Sanity loss
A human opponent attacks you with evident intent to do serious harm
You are in a car or other vehicle accident serious enough to pose a risk of injury
A human opponent attacks you with evident intent to kill
You kill someone in a fight
You are attacked by a supernatural creature, a friend, loved one, or person of solace
You kill someone in cold blood; you torture someone
You are tortured for an hour or longer
You are attacked by supernatural creatures - a horde or one gigantic one
You kill a friend, loved one, or person of solace

Witnessing violence
Sanity loss
You see a fresh corpse; you witness a killing
You witness acts of torture
You see a particularly grisly murder or accident scene
You see hundreds of corpses; you witness a large battle
You learn that a friend, loved one, or person of solace has been violently killed
You discover the corpse of a friend, loved one, or person of solace
You see a friend, loved one, or person of solace killed
You see a friend, loved one, or person of solace killed in a particularly gruesome way

Unnatural acts
Sanity loss
You experience unnaturally intense déjà vu, “missing time”, or hallucinations
You see a supernatural creature from a distance
You witness an obviously unnatural, but not necessarily threatening, omen or magical effect – a wall covered in horrible insects, a talking cat, or a bleeding window
You see a supernatural creature up close
You spend a week in solitary confinement
You witness a clearly supernatural or impossible killing
You witness or experience an obviously unnatural, and threatening, omen or magical effect – a cold hand clutches your heart, a swarm of bees pours out of your mouth
You discover that you have committed cannibalism
You are concious but helpless while some outside force possesses your body
You speak with someone you know well and who you know to be dead

Mythos Lore use - revelation or intuition
Sanity loss
Aspect of the Mythos is distant in space or time, or not immediately relevant
Mythos forms clear and present danger, reaches back far, wide implications
Clear and present danger to you or your loved ones
Shatters one of your Pillars of Sanity
Could destroy the world or is actively doing so, probably inevitably
Your drive is meaningless or doomed