Certain Fathoms is a 50+ page sci-fi horror module for Mothership, plunging players into the sludge-choked ruins of Welkin Campus—a long-forgotten AI research complex buried beneath Prospero’s Dream. Guided by Miranda, a rogue AI trapped in synthetic flesh, crews descend via the Black Elevator into a shifting labyrinth of experimental tech, corporate secrets, and unstable anomalies.
The Black Elevator is the only way in—or out. Each time the crew uses it, the elevator brings them to a new, randomized floor deep within the campus. No map, no control—unless they’ve recovered a keycode to a specific level. The deeper they go, the weirder and more dangerous things get. Anomalies distort reality. Breaches escalate the threat. Returning to the surface means backtracking through what they've discovered so far—and encountering who or what has discovered the crew.
Certain Fathoms is a 50+ page saddle-stitched zine with the following:
A depth-crawl megacomplex book with 20 floors, ranging from personnel- to industrial-scale, each with its own strange mysteries and unraveling horrors.
Four dangerous factions led by powerful remnants of Welkin Orbital, from the Loopers trapped in an eternal birthday party to the Custodians who keep the lights on - by any means necessary.
A replayable and repeatable gameplay loop, where destinations, anomalies, and random encounter breaches are rolled to create new situations with every delve.
40+ new prototype cybermods and slickware from the fine researchers at Welkin. Some are hidden away in secret chambers and lost labs, while others will have to be pulled from cold, dead hands.
A new patron NPC who'll guide you through the facility, as she herself uncovers her connection to the sprawling Welkin Campus.
Art by DC Stow
And that's not all:
New art from the likes of DC Stow, Amanda Lee Franck, Evangeline Gallagher, and more.
Easy-to-reference layout for quick reading at the table.
Hundreds of secrets and reality-breaking truths, from the real reason Welkin Orbital went under to the purpose behind the enigmatic YR-XII project.
Certain Fathoms is only the beginning of the crawl. Two expansion zines add a variety of new ways to play, from battling rival crews in the depths of the megacomplex to delving into Welkin's past for fame and fortune:
Digital Zine For digital divers. Get the complete PDF of Certain Fathoms and dive straight into the Sink from your screen or tablet. Perfect if you don’t need the print edition. You get:
Certain Fathoms (PDF)
Printed Zine + PDF The core book, in print. You’ll receive Certain Fathoms in full-color half-letter format, plus the PDF for easy reference. This is the entry point into the Sink. You get:
Certain Fathoms Zine
Certain Fathoms (PDF)
Starter Bundle For those who want a little more. You’ll receive Certain Fathoms in print and PDF, plus one Expansion Zine of your choice (Hostile Takeover or Viewer Discretion). A solid dive, but not the whole story. You get:
Certain Fathoms Zine
Certain Fathoms (PDF)
Expansion Zine + PDF (Choose One)
All-In Bundle The full depth-crawl experience. Everything we’ve created for Certain Fathoms, in one bundle:
Certain Fathoms (print + PDF)
Both Expansion Zines (Hostile Takeover + Viewer Discretion - 30+ pages of content)
Pamphlets + Bookmark (Otto’s Buy Bin + Procedure Reference)
Certain Fathoms Digital Soundtrack (MP3 + FLAC)
This is the complete Welkin package. If you want it all, this is the best place to get it.
Here's the breakdown of each tier and what you get:
Pledge Manager Access Want to back Certain Fathoms, but don't have the funds? Or want to see what all the fuss is about after the hype dies down? Pledge a $1 to get access to the Pledge Manager a few months after the campaign is over and select carte blanche (note, this will likely be more expensive than backing during the campaign!). You get:
Pledge Manager Access (Date TBD)
Retailer Copies Want a few copies of Certain Fathoms for your storefront? Get 6 copies of Certain Fathoms at wholesale pricing, with PDF included for store reference. Add additional copies for $10 each through the pledge manager.
Retailer Notes:
This tier is only available to verified brick-and-mortar or online retailers.
We’ll confirm store information after the campaign to ensure eligibility.
Each bundle includes PDFs for staff use (not for resale).
Additional copies may be added in the pledge manager for $10 per zine.
Expansion zines and other items may be available separately at wholesale rates after the campaign.
Your descents are broadcast for entertainment and, more importantly, profit. Sponsors meddle, fans demand spectacle, and you only get paid if you play along.
How many crew members does it take to operate an elevator?
Bookmark: Black Elevator Reference (Print + PDF) | $7
For a quick, at-a-glance reminder of the core procedures of Certain Fathoms.
Art Subject to Change
Gatefold Pamphlet: Otto's Buy Bin (Print + PDF) | $12
Otto Lykus is an enigmatic fence across the systems. He's taken a great interest in what's buried at Welkin—and is willing to trade strange esoterica for it.
The Current hums in steel veins.
Certain Fathoms Soundtrack (MP3 + FLAC) | $12
Over an hour of industrial, dark synth ambient tracks to coordinate with your crawl.
Your access to the depths of Welkin.
Patch: "Welkin Clearance" | $8 (Free for 48-Hour Early Birds)
As we hit certain thresholds, new unlocks become available to all backers:
Secret Levels are a series of add-on destinations found locked away from the main floors of Welkin Campus. Each is written by a guest collaborator and RPG luminary, and all of them are wonderfully weird.
Employee of the Month is a secret digital expansion to Certain Fathoms that offers a ruleset for running solo characters or crews through the depths of Welkin. Oracles, special mechanics, and more await.
Echo Chamber is another secret digital expansion to Certain Fathoms that explores a part of the campus completely untouched by time—literally. Explore the splintered past of Welkin Orbital in this foray through time and reality itself.
This year, we're trying something different. Nearly every Mothership Month project is part of a shared shipping initiative. That means:
One pledge manager. When Mothership Month ends, you’ll receive one combined pledge manager survey for all participating projects — our “mega pledge manager.” That means just one survey and one shipping payment for multiple projects.
One shipping charge. Because these projects will ship together, you’ll only pay shipping once, saving you money.
One fulfillment timeline. All participating campaigns are scheduled to ship at the same time, ensuring your rewards arrive together.
Two exceptions. Only two creators (Bombs Bursting in Air and Roach Motel) have opted out of this group fulfillment plan; their shipping will be handled separately. Why did they opt out? These two projects are very close to being ready to fulfill, and it didn't make sense to their teams to wait.
Estimated Shipping
Below is a table of estimated shipping prices based on weight. You can see at the bottom what the estimated weights are for different items. Prospero's Dream should be around the same weight (maybe slightly lighter) than the Mothership Core Set. Additionally, if you order several items you'll incur a small charge for additional items, which varies based on your country.
This does not include any applicable VAT or taxes. A reminder that these shipping prices are an estimate and its possible they will change based on global conditions beyond our control.
When will these projects ship? Our collective goal is to have all Mothership Month 2025 projects fulfilled before Mothership Month 2026 begins. Some projects are further along than others, so their timeline for digital rewards will vary. But we have roughly a year to fulfill before Mothership Month 2026, which gives everyone enough time to finish up and get their products to our warehouse.
What is Mothership Month?
Every year, Tuesday Knight Games and dozens of third-party creators launch new Mothership projects around a shared theme. This year’s theme (“The Dream Returns”) centers on Prospero’s Dream, the infamous X-Class back-world, black market space station. Each project ties back to the Dream in some way. Not only that, but we'll be opening up Prospero's Dream as a shared setting for all third-party creators going forward.
Get your exclusive Supply Pod!
This year we're changing up the Supply Pods. Now there is just ONE BIG SUPPLY POD. It's unlocked once all projects fund and it improves as we hit more group achievements. How do you get the Supply Pod? Back 5 or more projects at the physical level and get access to all the cool goodies.
Designer, Writer, Artist That’s me! I’ve been creating under the Grinning Rat Publications name for about five years now. Since the beginning, Grinning Rat has been all about sharing cool ideas, crafting great designs, and running fantastic games. By day, I’m a graphic designer—so when it comes to tabletop projects, I usually end up in the layout designer and writer seat. When I’m not doing that, I’m spending time with my family, playing way too much Magic: The Gathering, or reading.
Jarrett Crader
Development Editor Jarrett Crader has helped edit and develop and write and design and help bring into the world over 600 rpg books/modules/systems/pamphlets/pdfs/what-have-yous and keeps working on more all the time! He loves playing games and talking about games and thinking about games and making games and GAMES GAMES GAMES!!! When not GAMES!!! he can be found chilling with his partner and their cats and running Space Penguin Ink.
Stephanie Louise Guerreiro Lourenço
Copy & Line Editor
Colin Whitehurst
Musician Colin is a multifaceted creative with a background in visual media, including graphic design, animation, and video production. Outside of work, he dives into big cooking projects like making his own soy sauce, enjoys woodworking, and his current hyper-fixation is exploring sound through modular synthesis.
Evangeline Gallagher
Artist Evangeline Gallagher is an award-winning freelance illustrator from Baltimore, Maryland who has illustrated best-selling book covers, ENNIE award winning tabletop games, and countless flyers for local shows. When they aren't drawing, they can be found hanging out with lizards, getting too competitive about board games, or painting murals (but they are probably drawing).
Amanda Lee Franck
Artist Amanda Lee Franck is an artist and writer living in Chicago. The first RPG she ever ran (and first zine she ever published) was You Got a Job on the Garbage Barge. She has written and illustrated books for Games Omnivorous, Exalted Funeral Press, Mausritter, and many others.
DC Stow
Artist DC Stow is a fantasy enthusiast and self-taught illustrator from the mystical land of British Columbia, Canada.
════════ Guest Contributors ══════════
Alfred Valley
Thousand Empty Light, Dead Popes Alfred Valley is a klein bottle disguised as an analog game designer who is obsessed with photocopy machines. He has previously released Thousand Empty Light and Dead Popes for Mothership.
Sam Sorensen
Seas of Sand, Time After Time Sam Sorensen is a game designer, writer, editor, and graphic designer. He wrote the Mothership adventure Time After Time, the old-school setting guide Seas of Sand, and currently is working on real-time play-by-post roleplaying wargames, including Cataphracts and OVER/UNDER. He lives in Brooklyn, New York, and can usually be found at the Met.
Snow
Songbirds, .dungeon Snow is a writer and game designer living with her two partners and two cats in Chicago, IL, focusing on the queer and autistic experience in both her essays and games.
watt
Cloud Empress watt is a queer tabletop creator best known for the Panic Engine (Mothership compatible) ecological science-fantasy game Cloud Empress.
As part of Mothership Month 25, Grinning Rat and Hammer City Games are teaming up to bring you the best vat-grown sleeves on the market! Back both Certain Fathoms and Burnt Flesh & Borrowed Gloves to get even more good stuff:
