Dice Pools Revisited

Posted: 2022-09-17
Word Count: 1633
Tags: dice rpg third-system writing-rpgs

A few years (yes years) ago I wrote about dice pool mechanics in RPGs, and sketched out what I called the “Third System”.

Recently, after watching lots of isekai and shonen anime about overpowered heroes brushing off lesser foes, I started thinking about this system again. At this point the system is even sketchier than “Shadow Vale”; I have a bunch of ideas how to define Player Characters, but none I really like.


The system is geared toward settings where the Player Characters are Heroes with extraorinary if not supernatural abilities. Most of the NPCs are either Ordinaries who lack such abilities or Monsters who are by nature supernatural but unreasonable. Rarely the Heroes will run into Rivals, those with abilities and intelligence equal or greater than the Heroes but who usually work to thwart them.

To avoid the excesses of the rainbow of colored dice I proposed in the earlier article, I’m instead going to walk back one design choice: players roll most dice, but not all. When the GM plays characters as or more powerful than the Heroes the GM rolls dice. Ideally there won’t be many of those, and I’ll introduce rules to reduce the mental burden on GMs.

While the system borrows from the Year Zero Engine and Blades in the Dark, its initial inspiration was the boardgame Arkham Horror and its sequel Eldritch Horror. In those games players assume pre-defined characters and cooperate against randomly drawn events and monsters to avert a Lovecraftian apocalypse. Notably, players make Skill Tests to clear events and beat monsters: they roll a number of six-sided dice based on their Investigator’s relevant Skill, and each 5 or 6 rolled is a Success1.

Resolution Mechanic

When the players want to do something with a chance of failure, the GM first announces the level of difficulty and a Target Number (TN) to match:

Most tasks should default to Normal (5).

The player assembles a dice pool based on their innate Abilities and bonuses or penalties due to gear and external factors. The details of this are yet to be determined.

If, after penalties to the dice pool, the total number of dice is 0 (or lower), roll two dice and use the lower die (D) to determine success. Otherwise, use the highest die (D) to determine success:

If more than one die rolled a 6, the action was a Critical Success. Every 6 after the first adds to the action’s effect: extra damage in combat, additional positive effects, mitigation of a negative consequence, and so forth.

Using a Lua program which I won’t include because it’s derived from the one in “Yet More Year Zero Again”. I’ve derived the probabilities based on Difficulty and the size of the dice pool:

Dice 4+ 5+ 6 6x2 6x3
0d 25.00% 11.11% 2.78%
1d 50.00% 33.33% 16.67%
2d 75.00% 55.56% 30.56% 2.78%
3d 87.50% 70.37% 42.13% 7.41% 0.46%
4d 93.75% 80.25% 51.77% 13.19% 1.62%
5d 96.88% 86.83% 59.81% 19.62% 3.55%
6d 98.44% 91.22% 66.51% 26.32% 6.23%
7d 99.22% 94.15% 72.09% 33.02% 9.58%
8d 99.61% 96.10% 76.74% 39.53% 13.48%
9d 99.80% 97.40% 80.62% 45.73% 17.83%
10d 99.90% 98.27% 83.85% 51.55% 22.48%
11d 99.95% 98.84% 86.54% 56.93% 27.32%
12d 99.98% 99.23% 88.78% 61.87% 32.26%

From this we see that, under Normal (5) difficulty, a pool of two dice gives better than 50/50 odds and seven or eight dice gives about a 95% chance of success. Unlike the Year Zero Engine, there are no re-rolls in the rules as written.

The final system, if it’s ever written, will calibrate Ability scores with this in mind.


When Heroes and Ordinaries (or more subtle Monsters) engage in non-violent contests, use the rules above. That is, the GM represents the NPC as a Difficulty and possible Penalties. The player then assembles their Dice Pool, applies bonuses and penalties, and succeeds if they meet or exceed the Target Number on at least one die.

When Heroes and Rivals (or other Heroes) come into conflict, use the following procedure:


In the original “Player Rolls All Dice” conflict/combat system I originally sketched out, Ordinaries and Monsters attack as a single Horde. Each member of the Horde has a number of Health Points (HP) – 1 for cheap thugs, 2 or 3 for guards or mercenaries, more for monsters – which add up to a single pool of HP for the Horde. Likewise the Horde has a single Damage Per Hit (DPH) rating, from 1 to (typically) 4, based on their numbers and the strength of each individual.

Players will likewise have HP representing luck and/or magic that allow them to withstand counterattacks.

Each round of combat, the Heroes roll an Ability for combat; results depend on the level of success:

At the end of the round, multiply the number of Hits by the the Horde’s DPH, and let the players distribute the Damage among their characters as they wish.

As the Horde takes damage, the GM eliminates individuals, weakest first. For example, if Heroes do 7 HP of damage to a Horde of 10 guards (1 HP each) and a Captain (2 HP), only 3 guards and the Captain will remain. The other 7 aren’t dead; they’re unconscious, too weak to move, or simply playing dead until they can crawl away.

The GM can adjust the threat posed by NPCs in this system in multiple ways:

  1. Increase (or Decrease) Difficulty: Combat against veteran troops might be Hard, while combat against an untrained mob might be Routine.

  2. Impose Penalties: Certain foes might be tougher, quicker, or better armored than the average foe. Against them, the GM might reduce the dice pool by -1 or -2.

  3. Increase HP or DPH: The simplest way is simply to increase the number of individuals, increase the Horde’s DPH, or throw in tougher foes with more HP and a higher DPH.

  4. Increase DPH: A Monster – or an Ordinary with a special weapon – might do 2, 3, or more Hits with a single attack.

  5. Add Special Attacks: Monsters or experienced Ordinaries might have sophisticated tactics or special abilities that control the battlefield.

Armor and Weapons

Heroes and Rivals may wield better weapons that have a Damage Bonus that adds to the damage from rolling 6es. “Masterwork” weapons might provide a bonus to the Dice Pool as well.

Just like in the Year Zero Engine, Hero armor has an Armor Rating (AR). When a player wearing armor takes damage, the player rolls a number of dice equal to the AR, and subtracts one point of Damage for each 6 rolled. However, every Damage point absorbed reduces the AR by one point until the armor can be repaired.

Armor for NPCs is reflected in increased HP, for simplicity.

When Rivals Attack

When combat involves a Rival, use the procedure below:

The same procedure works if one Hero attacks the other.

  1. Under normal circumstances. Under the effects of Blessing a 4, 5, or 6 counts, while under a Curse only a 6 counts. ↩︎

  2. While I like the Year Zero Engine, Pushing Your Roll mitigates the low chances of success but incurring some mechanical consequence: attribute damage, Conditions, Stress, Darkness Points, etc. For now, I’ll trade rerolls for better chances with fewer dice, and fixed mechanical penalties for narrative consequences. ↩︎

  3. I.e. the Heroes in combat with the Rival. Admittedly a combat with multiple Rivals and/or a Horde can get as messy as a melee in a tactical tabletop game. Presumably one combat-oriented Hero would take on the toughest Rival, while the rest whittle down the Horde and/or lesser Rivals … just like in the cartoons. ↩︎