Writing RPGs is Hard, Part 3: Dice Pools

2019-10-05

Modified 2019-12-12

UPDATED (2019-12-12): Using the apparently official name for the Free League's house system: "Year Zero".

Reading the “quickstarts” for Mutant: Year Zero and Forbidden Lands1 has sparked some thoughts about the Untitled dice pool system I’m temporarily calling “The Third System”.

The Year Zero System

Mutant: Year Zero, from Free League Publishing2, uses a d6 dice pool mechanic:

  1. Assemble a pool of color-coded six-sided dice:

    • Base Dice equal to the base attribute being used.
    • Skill Dice equal to the skill rank, possibly modified by difficulty
    • Gear Dice for the quality of equipment being used.
  2. Roll all dice; the character scores one Success for every 6 rolled.3 Usually one will suffice, but sometimes extra successes activate extra effects.

  3. After the initial roll a player can “push” their roll: they reroll any Skill Dice not showing a 6 and any Base Dice or Skill Dice not showing a 6 or a 1. Any 1 from the initial roll or the new roll has the following effect:

    • Each 1 on a Base Die4 diminishes the Base Characteristic used in the roll; when a Characteristic hits 0, the character is Broken: beaten, exhausted, confused, or demoralized, and barely functioning. Each 1 also gives the character a Mutation Point (MP). Characters expend MP to activate their mutations.

    • A 1 on an Gear Die5 decreases the Gear Bonus for the gear in question by 1. A “Gearhead” (PC or NPC) can attempt to fix it but if they fail the bonus is stuck permanently where it is; at 0 trying to fix the gear will break it permanently.

    • Skill dice have no ill effects on a 1.6

  4. If a player rolls no successes, whether they push or not, the character doesn’t simply fail a task; they lose something. Mutant Year Zero recommends only rolling dice when something is at stake; by definition, a lack of successes means a definitive loss.

Subsequent games from Free League use the same basic mechanics with slight tweaks:

The “Third System”

What I was calling “Untitled RPG #1” and am calling “The Third System” counts 5 or 6 as successes. As originally stated it has no consequences for rolling other numbers. Also as stated before, each level of Difficulty subtracts one die from the player’s dice pool, because Players Roll All Dice in this system.

If the player ends up with zero dice, they could still attempt a Luck Roll: roll two dice, and both must show 5 or 6 to count as one Success. For each point below zero the total dice pool drops add one to the Luck Dice pool; again, all dice must show 5 or 6 to count as one Success.

In retrospect, subtracting dice and Luck Rolls are a bit difficult to explain. One morning at a coffee shop, I came up with a few other options to represent difficulty:

If only for my own sanity, here’s a summary of the above:

Type Color (suggested) Success Anti-Success other effects
Ability white 5, 6 -
Danger black 6 1 Complication if any Anti-Successes left
Doom red 5, 6 Doom if any 1s rolled
Fortune blue 6 -
Misfortune yellow? 1 -
Rival purple? 1, 2 NPC wins if Anti-Successes left over

This is way too many dice types and colors. I’d like to limit it to three, maybe Ability, Fortune, and Danger.

Compare and Contrast

The “Year Zero” system does sound simpler in comparison, if only because every die type works the same way and color only matters on a failure. Unfortunately, when only a 6 is a success players need to throw about twice as many dice. Below are numbers from the “Forbidden Lands Quickstart” and the corresponding percentages for successes on 5 or 6.

# of dice Chance of Success Pushed Roll “Third System” Success
1 17% 29% 33%
2 31% 50% 56%
3 42% 64% 70%
4 52% 74% 80%
5 60% 81% 87%
6 67% 87% 91%
7 72% 90% 94%
8 77% 93% 96%
9 81% 95% 97%
10 84% 96% 98%

In my system I was trying to avoid rolling more than 5 dice and rerolls for players to have a decent chance of success. In the Year Zero System a character has no characteristic lower than 2, and “average” is 3; skills and equipment merely add dice. In Traveller, by comparison, a player rolls 2d6 and suceeds on a total of 8 or more; without modifiers from attributes or skills they have a 42% chance of success. (This could happen if the character has “average” attributes and a skill level of 0, meaning trained in the basics but little else.)

Also note that in both the Year Zero System and my “Third System” players can “spend” successes for additional effects. From some brief simulations in AnyDice it appears a Year Zero System roll (without pushing) generates nearly the same distribution of Successes as “Third System” with twice the dice.

Mechanical differences also reflect different settings. In Mutant: Year Zero sterile mutants struggle for survival in a dying world. In Forbidden Lands adventurers cross into a cursed land seeking loot. Tales from the Loop and Things from the Flood take place in our recent past but filled with strange machines and unknown creatures. In Coriolis and presumably the Alien RPG characters brave the vacuum of space and alien worlds. In all these cases PCs’ biggest threat is the world around them. Without sufficient ability, training, and gear, chances of success are low.

The notional setting for “Third System” is a science fantasy post-apocalypse inspired by Miyazaki’s Nausicaa and other works, The Vision of Escaflowne, Thundarr the Barbarian, and especially the Netflix She-Ra series:

The Age of the Ancients ended abruptly and mysteriously. They left behind only forbidding monuments, incomprehensible artifacts, bio-engineered flora and fauna, terrible techno-organic monsters, and dangerous powers that sorcerers attempt to master.9 Many areas remain uninhabited or at least unexplored.

Over untold generations mankind rebuilt.

We rediscovered the secrets of farming, of shaping wood and metal, of harnessing wind and water. While this New World may not be as peaceful or as plentiful as the Ancient World of legends, we settle most of our differences without bloodshed.

In recent times despots from another world arrived to plunder this one. They build terrible engines of conquest and threaten our hard-won peace. They are yet few, but their numbers are growing and their weapons are terrifying. Our nations are divided; our leaders argue and do nothing. Who will defend us?

While post-apocalyptic, the premise is fundamentally optimistic. Ideally, player characters defend their homes and their world from rampaging monsters, conquering hordes, and power-mad sorcerers. They have special knowledge and training that gives them a huge advantage over conscript soldiers and mundane perils. Even outside their comfort zones they have a decent chance – 1 out of 3 – of muddling through most situations. Their opponents are beings as well or better trained than they are, threats from the Time of the Ancients, and new menaces from beyond the world they know. Thus players don’t need to roll dice so characters can climb a tree unless they’re under significant time pressure … and somebody or something is making them hurry. A guiding rule of the Third System is that characters – PCs and NPCs – always succeed unless another character opposes them10.

After seeing Forbidden Lands I kinda want to add a “Power Die”: a d12 (or in a pinch two sparkly pink d6s) representing the astounding effects of Ancient Artifacts11: 50% no Successes, 17% one Success, 17% two Successes, 8% three, 8% four. Intact Ancient artifacts might take time and effort to unlock, but once someone does it literally blows away common gear12, wonders of sorcery13, and the Empire’s “Nu-Tech”14.

It’s a cute idea, but early on I decided that intact Ancient Artifacts always work as designed and do what they’re told, even if that isn’t necessarily what the user wanted. Random and variable effects almost sounds like a Sorcery thing.

So for now, to the extent I’m working on this at all, I’ll stick with my original mechanics: Ability Checks where 5 and 6 are Successes, Difficulty modifiers to reduce the dice in Ability Checks, and Luck Rolls for cases where players still have a slim chance. Fortune Dice, Danger Dice, and Opposed Rolls will remain in my back pocket unless I need them. I’ll only use Doom Dice for Sorcery or similar Faustian bargains, and only if there’s a compelling case.

Postscript: While developing the setting (and rewatching She-Ra), I’m thinking about adding yet another faction, the Dominion of Light. They’re a faded but still dangerous empire in which immortal, magical beings rule “benevolently” over human slaves. Just to deconstruct even further the anti-technology and pro-aristocracy biases of most fantasy.

Post-Postscript: Also, I want PCs to be heroes of the people (emphasis: of the people), not stereotypical murderhoboes, the setting’s newest warlords, or the ultimate conquerors.15 How to discourage the Evil Option when a) player characters are effectively superheroes and b) players and GMs can do whatever they want with my work, I don’t know. Hopefully I’ll think of something less clumsy than Exalted‘s “everyone instinctively hates Exalts”. Two evil empires and a lot of angry villagers might do the trick … or it might not.


  1. Well, part of it; it’s over 100 pages, not including the intro adventure. ↩︎

  2. Also known by their native Swedish name “Fria Ligan”. ↩︎

  3. Custom dice replace the 6 with a radiation symbol. ↩︎

  4. Custom Base Dice replace the 1 with a biohazard symbol. ↩︎

  5. Custom Gear Dice replace the 1 with an explosion symbol. ↩︎

  6. Custom Skill Dice have no special symbol for 1. ↩︎

  7. Custom Forbidden Lands dice use crossed swords in place of a 6, and replace the 1 on Base and Equipment Dice with a skull. ↩︎

  8. See a future post for more – Future Frank. ↩︎

  9. Sorcerers gather power from relics and fragmentary knowledge of the Ancients. Other forms of “magic” may exist, and derive from other sources. ↩︎

  10. Or they’re doing something foolhardy if not blatantly impossible. ↩︎

  11. More-than-sufficiently-advanced technology of a vanished “Crystal Spires and Togas” civilization. ↩︎

  12. Early Modern with anachronisms: no gunpowder weapons, higher literacy rates, better engineering, much better medicine. ↩︎

  13. Found biotech and bits of jerry-rigged Ancient tech, mostly reserved for sorcerers and those who can afford them. ↩︎

  14. Equal parts dieselpunk, pulp retro-future, and applied mad science. ↩︎

  15. SF author Norman Spinrad calls this last option the “Emperor of Everything” plot, and brutally – but alas too subtly – satirized it in his novel The Iron Dream. ↩︎