GURPS: Jazz Age Mythos - an unofficial conversion/setting

Some of you may be interested in my latest attempt to bring Call of Cthulhu over to GURPS. Essentially, this is a setting guide for the 'Jazz Age' (actually I cover 1919-1939) with some new material for playing Cthulhu Mythos investigators using GURPS.

The major changes/features are a different way to look at Fright Checks/Sanity Rolls. My system breaks the Fright Check itself into two level of severity depending on the source: Stress Checks for 'normal' frights such as gory scenes, ghosts and other 'mundane' horror; and then the more mind-shattering Sanity Checks which are caused by insights into the true nature of the Cthulhu Mythos.

I also added a way to make increasing knowledge of the Cthulhu Mythos a mixed blessing. Knowledge of the skill Hidden Lore: Cthulhu Mythos is essential to counter the machinations of the Mythos followers, but a successful roll will identify a Mythos encounter as being such, and thus potentially promote a Stress Check to a Sanity Check.

My main aim, however, was to give players a believable setting in which their 1920s investigators could operate. I am aiming for an immersive environment where characters react to the narrative as much as to the mechanics.

As always, comments and suggestions are welcome.


  • GURPS CthulhuPunk uses fright checks like this (pages 45 and 46):

    Your normal roll target (Will, Reflexes etc) is halved and capped at half IQ+2. For example, someone with IQ 12 and the Unfazeable advantage rolls vs 8. For "Mythos" scares, like Hounds of Tindalos etc. Normal scares (dead bodies etc) work normally.

    And, if you critically fail a "Mythos" fright check, you permanently lose one will (in other words, you gain a level of Weak Will disadvantage).

    All that said, Chaosium Sanity™ has made me uncomfortable for a while as an uninformed and comedic depiction of serious mental health issues, and GURPS' implementation is close enough to share some of that same criticism.
  • GURPS CthulhuPunk isn't a supplement I have, unfortunately, not being a fan of post-1920s settings for the genre. That said, I am sure that the idea of splitting the Fright Checks is not new. I'd be surprised if I hadn't seen the idea somewhere online - these things rarely spring from nowhere.

    I don't cap Sanity Checks other than the 'Rule of 14' and having a maximum Will roll of 20 (as per the usual GURPS rule conventions). Instead, I have a two-tier table system. The Stress Check table results in more short-term effects and is similar to losing Fatigue instead of Hit Points. I kept in mind the reactions of characters in all those horror films and tried to model that.

    I agree that the usual GURPS Fright Check table results are 'clunky' when it comes to depicting mental conditions, but you're always going to have that problem when trying to depict psychological problems mechanically in an RPG (in the same way, physical injuries and diseases are fairly crudely modelled). I have approached psychological trauma somewhat differently and developed a list of Mental Conditions that I then defined with GURPS Disadvantages (a combination of Mental and Physical). More pertinently, my system encourages reinforcement of existing conditions rather than the 'scattergun' approach of picking up a wide and disparate variety of conditions each time a roll is failed.

    I have experience of mental health nursing (on both sides of the 'counter') so tried to apply at least some of this to the supplements. However, when all is said and done, playing characters with mental health issues is more down to roleplaying than to game mechanics.
  • edited June 2018
    GURPS CthulhuPunk isn't a supplement I have
    I understood that but that's why I paraphrased the way it does "Mythos" Fright Checks. So that you could compare it to your own work without having to buy it.

    I like it though. It also has stats for Mythos enemies and conversion rules for CoC.
  • Very good. I would find it sensible to play this type of GURPS. The system in full-body interaction with the setting would be interesting to figure out.

    I have minimal experience with GURPS, but significant experience with Call of Cthulhu; from this viewpoint I like the way you break down the campaign setting and its expectations. Particularly, I like that your campaign focuses on the long-term developments and implications of living in the Mythos setting, rather than lethal one-shots. I've always felt that CoC does a mediocre job at best in being a vehicle for horror storytelling in the literary sense, but that there is potential in the idea of delving in the setting in a slightly less mission-based context. It provides more interesting hooks for horror scenarios in the long term if the player characters are allowed to develop organic ties and projects in the milieu.

    Also, stable-based play - definitely a core element for campaign play of CoC.

    All in all, considering that I find BRP to be one of the stupidest rpg systems ever, this is vastly superior to the original as far as I'm concerned.

    A rules-question: how do you envision GURPS point games to be involved in the campaign? Will character points be gained as XP for adventuring? This being stable-based and in a genre where study is very much an element, can characters use the GURPS study rules to e.g. learn spells, improve their credit rating or do other beneficial downtime activities?
  • edited June 2018
    Thanks for the praise, it's always nice to find your work appealing to someone else.

    Points will be gained in a somewhat similar fashion to the way that CofC hands out Sanity for completing missions and thwarting the powers of the Mythos, only on a much lower scale. I'm thinking maybe 1/5th the maximum SAN award which would mean around 2 or 3 points per scenario. My usual GURPS XP awards give 1 point for playing, 1 point for decent roleplaying, 1 point for a successful outcome to the scenario, and a bonus if the player or character really shone. In most cases, I tend to award 3 points per game.

    GURPS study rules (B292) will very much apply to learning spells and Hidden Lore: Cthulhu Mythos, but other claims of learning 'free' skills from time investment will be treated on a case-by-case basis. I might allow it if a player plays it out, especially for the non-playing 'pool' characters.

    A variation will apply to recovering from Mental Conditions acquired as a result of failed Sanity Checks. This aspect of the game will be somewhat different to a normal GURPS campaign in that I expect players will need to use at least some of their points to 'buy off' their Fright-Check-acquired Disadvantages. As the campaign goes on this may provide diminishing returns but there is always the option of benefiting from taking the character out of the spotlight for long-term treatment ('curing' 1 point per month) which does not require points to be spent.
  • a successful roll will identify a Mythos encounter as being such, and thus potentially promote a Stress Check to a Sanity Check.
    Couldn't this rule encourage players to pretend that a Mythos encounter isn't a Mythos encounter, in order to get the "discounted" sanity loss?

    I think this kind of Mythos awareness (not the same thing as useful Mythos knowledge, for which a GURPS skill is a good fit) should be freely inflicted to the players and that, in a game about confronting the Mythos, it should be without mechanical adverse effects.

    Scary encounters could be either mundane, with a Stress Check, even with a Mythos origin (e.g. the bloody victims of a human sacrifice in a cultist hideout near the port), or unnatural, with a Sanity check, even without understanding much of their origin (e.g. the unimaginably old and strangely corroded remains of almost-human sacrifices in a buried prehistoric temple with suggestive cave paintings).

    Remove the choice, and you'll remove the possibility of silly tricks.
  • edited June 2018
    Thanks for the interest and input.

    imagine most players will certainly wish to pretend that an encounter is not with the Mythos, but the decision is not really in their hands. If the GM has decided that an encounter is Mythos-based (usually encounters with Mythos creatures or their immediate effects) then the roll against characters' Cthulhu Mythos skill is made. Meta-gaming pretending that Deep Ones are ugly pearl divers won't work if the character makes the Cthulhu Mythos roll. The dice and character's skill level make that decision.

    This is a deliberate ploy. New characters will genuinely not realise that Mythos experiences represent the existence of a whole raft of extra-terrestrial godlike beings. It is this knowledge that I see as key to the real horror of the Mythos - man is insignificant and Earth is simply a plaything of unimaginably irrational creatures against whom man's defences are nothing. Deep Ones are scary aquatic monsters (Stress Check), but it is even worse to know that they are a just the tip of the Mythos iceberg.

    Your example of a sacrifice scene would normally be dealt with a Stress Check, no matter how unnatural the setting. The point of Stress Checks is, after all, that the character experiences something that is terrifying but able to be rationalised. However, if the observer recognises that the robed man is chanting a spell to summon a Mythos being then this is further proof that the Mythos is real, with all the mind-blowing horror that this involves and thus a Sanity Check. Not understanding what is being chanted (failed Cthulhu Mythos roll) takes it back to being a Stress Check.
  • I don't think that it's a silly trick, though. Playing Call of Cthulhu is inherently an ironic exercise, just like something like Paranoia, because the players and the characters have such disparate perspectives on their experiences. Where the player expects supernatural and does not get unhinged by it, for the character it's the other way around: they have a cognitive interest in disbelieving the supernatural.

    Plus, it's ultimately a fool's errand to try to make sense of the assumed psychological model of CoC - it's not real, it's not realistic, it's just a genre conceit. That's just how it works.
  • edited June 2018
    No, it is absolutely the logical thing for a player to claim. 'How would my PI know it is anything to do with the Cthulhu Mythos? Why am I scared of what looks like a guy wearing a loose rubber suit?' In most cases they would have a real point.

    That's what Fright Checks are all about, of course, and why I use the identifying skill roll; 99.99% of people in the gameworld would see a 'dragon'. That would freak them out but legends of dragons have been around for millennia. Wow, they're real. Scary but not exactly mind-shattering.

    However, that 0.01% of folk who are able to make a Cthulhu Mythos roll recognise a hunting horror when they see it (whether they want to or not). If hunting horrors are real then maybe all that other stuff in the book was real as well.

    The creeping knowledge that the Mythos is a real thing is where my game's Stress/Sanity line is drawn. Yes, it is certainly an artificial conceit based on Lovecraft's writings, but it makes a nice division for my purposes - you have scary but Earthly on one side, and terrifying and otherworldly on the other.

    Of course, one possible power-gamey option for a Delusion might be that everything is normal and thus the character doesn't need to make further Fright Checks. I'd possibly allow this on the surface but inform the player that their character still makes checks and collects Mental Conditions as normal, they just don't necessarily manifest them. It would be tricky, but I might deal with it by deepening the Delusion until the character begins to completely disassociate themselves from the world. It's an interesting possibility but one I'd allow for the right player.
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