John Carter of Mars RPG Core Book: What Barsoom Fans Get

Quick answer

The John Carter of Mars RPG core book is the right first purchase if you want a self-contained 2d20 game of swashbuckling adventure on Barsoom and you plan to run or play it rather than just read it. If you already own another 2d20 game and only want lore, or you prefer a generic rules-light system, the core book is a harder sell. Buy the core book first, then add supplements only after your group has played a few sessions.

Edgar Rice Burroughs wrote eleven Barsoom novels, and the John Carter of Mars RPG is built to let you play inside that pulpy, sword-and-planet world rather than merely retell it. The core book is the entry point: it carries the setting, the 2d20 rules, and the character options in one volume. That makes the first buying decision simple, but it also means the core book is doing a lot of work.

This guide covers what the core book actually offers a Barsoom fan, how the 2d20 system shapes play, and where the real trade-offs sit. It also flags when a different purchase in the Modiphius US catalog might serve you better.

What the John Carter of Mars RPG core book contains

The core book is the complete game in one purchase: the 2d20 rules, character creation for Earthborn and Barsoomian heroes, the major factions and peoples of Mars, and the Game Master material needed to run adventures. For a Barsoom fan, that means you can build a Red Martian warrior, a Green Martian, or a displaced Earthman and start playing without a second book.

Because the setting is baked into the same volume as the rules, the core book doubles as a lore reference. That is a genuine advantage for readers who love Burroughs' world, but it also means the book is dense. Expect to read it in chunks rather than absorb it in one sitting.

• Check the product page for the exact edition and format before buying, since core books are sometimes reissued.
• If you only want to read about Barsoom, a novel or setting book may serve you better than a full RPG.

How the 2d20 system plays on Barsoom

John Carter of Mars uses Modiphius' 2d20 system, the same engine family behind several other games in the catalog. In practice, 2d20 rewards momentum and risk-taking: you roll a pool of d20s against a target number, and you can spend resources to push results further. That suits Barsoom, where heroes leap, duel, and improvise rather than grind through tactical combat.

The trade-off is that 2d20 is a real system with real moving parts. If your group already knows 2d20 from another Modiphius game, you will pick it up quickly. If your table prefers very light rules, the core book will feel heavier than expected.

• Read the momentum and threat rules carefully before your first session; they drive most of the drama.
• If your group already plays another 2d20 game, reuse that familiarity instead of relearning from scratch.

Who the core book is actually for

This is a game for people who want to play in Burroughs' Mars, not just borrow its aesthetic. If your group enjoys heroic duels, airship chases, ancient ruins, and faction intrigue, the core book gives you the tools and the world in one place. It is also a strong pick for a GM who wants a setting with recognizable factions and a clear tone.

It is less suited to groups that want a generic toolkit they can reskin. The core book is committed to Barsoom, and that commitment is the point. If you want a flexible system first and a setting second, look at a different game in the catalog.

• Decide whether your group wants a setting-first game or a toolkit-first game before you buy.
• A single enthusiastic GM can carry the core book for a whole table.

Supplements and where to go after the core book

The core book is designed to stand alone, so you do not need supplements to start. Once your group has played a few sessions, supplements become useful for expanding regions, factions, or adventure material. The practical rule is to buy the core book, run it, and only then decide which gaps you actually feel at the table.

Buying supplements before you have played risks duplicating material you already own or chasing content your group never uses. Let actual play tell you what you need.

• Run at least three sessions before buying any supplement.
• Note the specific thing you wanted mid-session; that note is your buying list.

Where the John Carter RPG sits in the wider catalog

If you are weighing this against other Modiphius US titles, the comparison is about tone and commitment. Dune - Adventures in the Imperium – Core Rulebook Standard Edition is another 2d20 game with a strong setting, but it trades sword-and-planet adventure for political intrigue. Blade Runner RPG Starter Set is a boxed entry point built around investigation and the Year Zero Engine rather than 2d20.

For a Barsoom fan, the deciding factor is usually the setting itself. If you want John Carter's Mars specifically, the core book is the direct route. If you want a different flavor of science fiction, one of those alternatives may fit your table better.

• Compare the setting promise first, then the rules engine.
• A starter set is often the cheaper way to test a system before committing to a core book.

Decision rules for buying the John Carter core book

• You want to run or play on Barsoom: Buy the core book first. It contains the setting and the 2d20 rules in one volume, so no supplement is required to start. Start here if Barsoom is the reason you are interested.
• You already own another 2d20 game: You will recognise the engine, but the Barsoom content is still new. Buy only if you want this specific setting, not just another 2d20 rulebook. Skip it if you only want the rules.
• You want a lighter or more generic system: The core book is committed to Barsoom and uses a full 2d20 ruleset. A different game in the catalog will likely fit better. Choose a toolkit-style RPG instead.
• You are unsure about supplements: Play three sessions before buying anything else. Note what you actually reached for during play and buy only that. Let play, not browsing, drive supplement purchases.

Catalog facts worth knowing

• Dune - Adventures in the Imperium – Core Rulebook Standard Edition: Winner of the Gold 2022 ENNIE Award for Best Writing, and a 2d20 game set in the Dune universe. If you want a 2d20 game with a different flavor of science fiction, this is the closest catalog alternative to John Carter's sword-and-planet adventure.
• Blade Runner RPG Starter Set: A boxed set with a 32-page condensed rulebook, the Electric Dreams case file, four pre-generated characters, and a map of Los Angeles, using the Year Zero Engine. A lower-commitment way to test whether a cinematic, investigation-focused sci-fi RPG suits your group before buying a full core book.
• Mindjammer: Transhuman Adventure in the Second Age of Space (For Traveller): A 384-page hardback transhuman science-fiction setting for the Traveller RPG, with rules for starships, organisations, and culture operations. Shows how far the science-fiction RPG range stretches beyond Barsoom, useful if you want a space opera toolkit rather than a fixed setting.

Is the John Carter of Mars RPG core book right for you?

Best for

• Fans of Edgar Rice Burroughs who want to play, not just read, in the Barsoom setting
• Groups that enjoy heroic, swashbuckling science fantasy with duels, airships, and faction intrigue
• GMs who want a setting and rules in a single core book

Not for

• Players who want a generic, setting-neutral rules toolkit
• Tables that prefer very light or rules-free systems
• Readers who only want Barsoom lore and have no interest in running a game

If Barsoom is the draw, the John Carter of Mars RPG core book is the straightforward first purchase: setting and 2d20 rules in one volume, ready to run. Buy it, play a few sessions, and let the table tell you whether a supplement is worth adding.