A Binomial Dice Pool OSR RPG

In my previous blog post, I outlined the basic design and play philosophies I’d like in a basic fantasy game. I approach all this from the perspective of the GM and the player. I want easy, intuitive rules that do not require page flipping. I want players to be able to make fun characters, but I don’t want the options to cause player choice paralysis or overburden the GM.

Now let’s get into some of the basics.

Primary Attributes

The Primary Attributes should be familiar to anyone who plays RPGs. Presence may be the only one that is slightly different. It is similar to Charisma, but includes supernatural elements. It typically is not used in social encounter rolls, as I believe those situations should be roleplayed rather than roll-played.

Might: Represents a character’s physical strength.

Vitality: Represents character’s overall bodily makeup, stamina, and constitution.

Agility: Represents a Character’s dexterity and hand-eye coordination.

Wits: Represents a character’s intelligence, wisdom, and problem-solving abilities.

Will: Represents a character’s resolve, determination, and mental fortitude.

Presence: Represents an amalgamation of a character’s attractiveness, personal magnetism, and even supernatural aura.

Primary Attributes vary in Rating from 1-5 typically for Medium sized creatures, though it is possible to max out at 6 by taking certain Traits.

Secondary Attributes

Secondary Attributes are calculated by adding together particular Primary Attributes.

Health = 5 + Vitality + Will

Defense = Vitality + Agility + Armor

Perception = Wits + Will

Skilled Bonus= A number determined by choices made in character creation

The next two Secondary Attributes are only for characters that are Magic Users or Adherents, respectively.

Magic = Wits + Will

Mystic Aura = Will + Presence

You’ll notice there is no initiative. I’ll cover how that works later.

Rolling Dice and Making Checks

The Dice

The dice are binomial dice with each side indicating a number of successes or a failure (represented by a 0). All dice are D8s.

Yellow dice have have 4 sides with 0 successes and 4 sides with 1 success, meaning rolling a yellow die is like flipping a coin–a 50% chance of success or failure. Blue dice are numbered in a way to be the statistical equivalent of rolling two yellow dice. The green dice are numbered so that they are the statistical equivalent of rolling 3 yellow dice.

Because the statistical chances of getting successes (or heads, if you think about it like flipping a coin) carry accurately across all three dice, you may mix and match them when rolling.

So, as an example, if you needed to roll 6 dice for an Attack, Defense, or other Check, you could:

Roll 6 Yellow dice (1+1+1+1+1+1+1=6)

This roll garnered 4 successes.


3 Blue dice (2+2+2=6)

This roll netted 4 successes.


2 Green dice (3+3=6)

This roll has 3 successes.


1 green die, 1 blue die, 1 yellow die, (3+2+1=6) etc.

This roll garnered 3 successes.

Just remember yellow (1x) + blue (2x) = green (3x)

After rolling, simply add up the faces showing and this is your total Successes. In this way, the number of dice rolled can be cut down by up to a third. It also removes the need to sort dice like many dice pool mechanics require; Just add up the faces and that is the number of successes rolled.

Successes are measured against a Difficulty Rating (DR) of the task at hand.

Very Hard5
Nearly Impossible6

Your Rating in an Attribute is the number of dice you roll for that Check (Plus any modifiers. Modifiers always add or subtract dice, not the result). This also means that, on average, you will get half the number of dice you roll in successes. In this way, you can easily gauge your own chances of successfully completing a task if you know its Difficulty Rating (DR). You want to meet or exceed a Difficulty Rating.

Opposed Rolls

Not all rolls are against a Difficulty Rating. Attacks against an opponent, for instance, are Opposed Rolls. An Attack roll is measured against a Defense roll. If the Attack is higher, the damage is the difference between the two results. If the Defense is higher, the Attack did no harm. Other Opposed Rolls could be Might versus Might or a Spell effect versus a target’s Will Rating.

Extra Successes

On Attack rolls, extra successes above an opponent’s Defense roll result equal the amount of damage done. However, extra successes on other rolls may have other uses. Many Spells will allow the caster to spend the extra successes to Empower the spell. See each Spell’s description for specifics.

Failed Rolls

On most rolls the GM has players make, a Failed Roll (either a DR not met or a Defense not bested) means the action attempt failed. Failed Rolls on Spells have an additional repercussion. However, players always receive 1 Resolve for failing.


Spell rolls that don’t meet the DR of the Spell cause Health damage to the caster equal to the difference between the roll and the DR. The caster also receives 1 Resolve.


Resolve is a meta-currency players receive when they fail Attack and Check rolls. Although they failed their action, they gain 1 Resolve to do better in the future. Resolve may be spent in a couple of ways:

  1. Spent on a one-to-one basis to cancel incoming damage.
  2. Spent on a one-to-one basis to add additional dice to a pool before it is rolled.

Characters are given 3 to 5 Resolve (GM’s choice) at the beginning of each game session. Any unused Resolve carry over to the next session. There is no limit to how much Resolve a character stockpiles.

Modifiers to Rolls

Player rolls consist of rolling dice equal to the Attribute associated with the action they are trying to take. These rolls can (and often) be affected by modifiers that change the total number of dice rolled. These include:

Skilled Bonus: Characters have a bonus to skills they are particularly proficient in. Anytime a character attempts an action they are Skilled in, they add their Skilled Bonus to the total number of dice they roll.

Advantage/Disadvantage: The GM may decide certain situations call for bonus dice (Advantage) or penalty dice (Disadvantage). This bonus or penalty is always +/- 2.

Spending Resolve: Players may spend resolve to increase the number of dice they roll for an Attack or Check roll. Resolve cannot be used to boost Defense, but it can be used to cancel out incoming damage on a 1-to-1 basis.

Focus: Focus is a special Action that benefits a subsequent Action in the same Round. For example, a player choosing a Slow Turn may use the first Action to Focus. The second action receives a +2 bonus. This could represent aiming prior to a ranged attack, looking for weaknesses in defense before a melee attack, or taking extra time casting a Spell to get the verbal and somatic components correct.

Cover: Characters in some kind of cover are harder to hit and gain Advantage on their Defense roll.

Elevation: A character shooting down on targets at a lower elevation gain Advantage on their attack. Players from a lower elevation shooting up at targets at a higher elevation suffer Disadvantage on their attacks.

Ranged Weapons in Melee: Ranged weapons in melee may be used, but suffer Disadvantage.

Different types of modifiers can stack, however, no single roll can be modified by more than +10.

Lastly, for those who wonder if the dice system statistically makes sense (ie, is a blue die truly the same as rolling two yellow dice?), yes! But here’s a breakdown of the numbers:

Yellow Dice: 4 sides have 0’s and 4 sides have 1’s.

Thus, there is a 50% chance of rolling 1 success. (4/8 = 1/2 = .50 = 50%)

Blue Dice: Blue dice are the statistical equivalent of rolling 2 Yellow dice.

Blue dice have:

2 sides with 0’s. (2/8 = 1/4 = .25 = 25%)

4 sides with 1’s. (4/8 = 1/2 = .50 = 50%)

2 sides with 2’s. (2/8 =1/4 = .25 = 25%)

Thus, you have 25 % chance of getting no successes or 2 successes, and a 50% chance of rolling 1 success.

Green Dice: Green Dice are the Statistical equivalent of rolling 3 Yellow dice.

Green dice have:

1 side with a 0. (1/8 =.125 =12.5%)

3 sides with 1’s. (3/8 = .375 = 37.5%)

3 sides with 2’s. (3/8 = .375 = 37.5%)

1 side with a 3. (1/8 = .125 = 12.5%)

Thus, you have a 12.5% chance of rolling no successes or 3 successes, and a 37.5% chance of getting 1 or 2 successes.

You can check these chances with Anydice or any Coin Flip calculator online.

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