I'm trying to evaluate the degree to which Fate of Cthulhu is worth my time, money, and either waiting time or hassle related to buying specifically the PDF (I have no need for the dead tree version which is currently bundled with it). This evaluation hinges on two main factors: the Condensed rulebook (which seems worth it), and the handling of time travel (about which I'd like to find out more).

I have seen short reviews indicate that the book offers good ways to handle the usual concerns of time travel such as paradoxes. However, what that actually means and how useful that is to me depends on an unstated assumption/context, which I'd like to know about:

Which model of time travel has been chosen when writing the setting and ruleset, and which of the common switches and toggles related to that model are in what states? Does it even have a coherent model of time travel? (After all, some franchises resort to 'solving' paradoxes by way of a timey-wimey ball.)

If the heart of the question looks ambiguous, here's a bit of a clarification: when I talk of the models of time travel, I mean those such as in this simplified list. Note that the list is just a starting point; it doesn't go deep into exploring switches and toggles, e.g. how the Sensitive History model can be made more consistent and playable by use of Achron-style meta-time and change-propagation principles, or how adjusting the 'speed' of time waves can produce different scenarios and overall feel of a story/campaign/game.

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    \$\begingroup\$ You might start with “Does Fate of Cthulhu use a consistent model for time travel? If so, which one?” (It’s not a given that it does.) \$\endgroup\$ – SevenSidedDie Nov 8 '19 at 15:06

The writing up of the temporal cosmology in the book is neither detailed nor complete (and even outright whimsical in places), but certain things can be concluded from the bits scattered throughout the book. In general, the time model is presented in a way consistent with a single malleable history, where any change to the past will erase the initial iteration of the timeline, as exemplified by this statement on page 75:

Thank you for killing us all in a bright flash of arcane physics so that we may live again in a world that knows no such horrors.

It is also preceded by a statement that time travellers are becoming ontological orphans, i.e. the changes they do have no retroactive effects on themselves, and thus after travelling back they remember a previous iteration of the timeline, not the current one:

Any changes you make in the past will affect the future, possibly even preventing some important events in your life. That’s okay. Your subjective past does not change, even though you’ve essentially annihilated your old timeline in favor of the new one.

This is also confirmed on page 78:

THE FUTURE CANNOT OVERWRITE THE PAST From the observer’s point of view, the future exists only as potential. Subjective time isn’t affected by events that haven’t happened yet. Even as time moves forward and probabilities collapse into certainty, the past of the observer is unaffected.

Also, as per Cycle of a Timeline (starting on page 220-235) a degree of rubbery historical inertia is in play, though probably more akin to river water flowing around a rock: making changes to history does lead to reshuffling of some things, but they still 'strive' to lead to the same end result in the far future, at least initially.

While advocated from a dissociative perspective, the book nonetheless leans towards a chaotic-time-like idea that a timeline should not be revertable to its previous state (page 225):

DON’T CHANGE THINGS BACK When you change a catalyst, don’t walk it back to its original state. Why? Because the fun of the timeline is changing the timeline.

What seems a bit unclear is whether time jumps are done as a single unit even when multiple people jump together, and whether changes propagate throughout the timeline 'instantly', or at some Achron-style 'delay', allowing multiple jumps from the same iteration of a timeline into an earlier point within it. Page 233 gives ambiguous evidence that either a delayed (or, more trickily, gradual) propagation is in play, or single-unit jumps are possible, or both:

Early in a campaign, especially during and immediately after the first adventure, the people sent back after the heroes will be from the same or a very similar future. Keep these NPCs mostly the same, with only small differences. Convey that the future has only started to change.

There is evidence that propagation speed has a ratio of approximately 30:1 or higher, since it seems the future humans can occasionally send someone back for the sole purpose of updating their agents about what the current situation is like, on page 77:

We might send someone back to check on you periodically. We won’t know if there are changes, but you will, so after they brief you on what the future is like, you should have a good idea of what’s happened.


Have you found and read this review of an alpha version of the Kickstarter product?

I'll just go by your linked list of paradigms. The review appears to reveal that history in Fate of Cthulhu is either malleable or sensitive, and it describes the specific game mechanics which govern time travel in play.

As you play, you track [on the Timeline Sheet] the PCs successes and failures with regards to set tasks: did they take the relic, or did they hand it off to the villain in exchange for their lives? Did the kill the cultist, or did they “accidentally” post a missing ritual online? These all impact the timeline, and can either speed up or slow down the oncoming apocalypse.

Fate of Cthulhu handles this with a “Timeline Track”, which is tied to a sheet of all of the known events leading up to the Elder God Apocalypse. Once it’s full, the timeline is impacted by which side “won” that round, with the PC’s having the goal of stopping the apocalypse…or at least making the future a little bit better.

FoC rules in this Kickstarter preview version come with:

a spell that stops time on a target


limited precognition

Lastly, while this may or may not be directly related to time travel,

The Corruption Clock [...] tracks how much Corruption you have gained and how much time you have (so to speak) before something goes wrong. We get to see Corrupted Aspects (a way to track your permanent Corruption), as well as Corrupted Stunts (which work like Mega Stunts in Atomic Robo, but come at a cost).

Whether the timeline is under one of the single or multiple paradigms isn't addressed with game mechanics, but the point of view suggested by the review seems to point to "if there are multiple timelines, the player characters don't know it." They seem to be trying to fix their own timeline. However, the review does say that this early version of FoC provides, as setting material, "multiple timelines for each of the Elder Gods."

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    \$\begingroup\$ It seems the review's info is rather inconclusive. Oh well. Thanks for the effort. \$\endgroup\$ – vicky_molokh- unsilence Monica Nov 10 '19 at 10:35

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