The D4 Pool System

2025-06-08

Replacing the d20 in 5e (or powering your next RPG)

A bell‑curved dice‑pool that merges attack and damage, streamlines actions, and keeps the spotlight on meaningful player choices.

Why look beyond the d20?

The classic d20 roll‑high mechanic is fast and familiar, but its flat probability curve can feel swingy—critical hits and whiffs occur with equal likelihood for novice and expert heroes. A dice‑pool of d4s shifts the curve toward the average, rewards expertise with more consistency, and opens the door to some elegant mash‑ups of attack, damage, and action economy.

1. Building your Dice Pool

Start with your relevant ability modifier. A Strength +3 means three dice.

Add your proficiency bonus if you’re proficient in the task.

Example: A 5th‑level fighter with Str +3 and proficiency +3 swings a longsword ⇒ 6 d4. Roll all the d4s and total them. If the sum ≥ the DC/AC, you succeed.

Skill Checks

Because untrained characters roll only their raw ability dice, skill selection matters more: the bell curve makes 2 d4 notably weaker than 5 d4.

2. Folding Damage into the Roll

For attacks we append the weapon’s (or spell’s) damage die after building the pool.

Dice Pool = ability dice + proficiency dice + damage die Damage = (total − target AC) • minimum 0

Longsword swing: 6 d4 + 1 d8 vs AC 16. Roll: 4 + 3 + 3 + 2 + 4 + 2 + 7 = 25. 25 − 16 = 9 slashing.

Misses become glancing blows that still feel impactful, and high armor always absorbs something.

3. Risk Dice: Trading Damage for Accuracy

Spells (and heavy‑hitting maneuvers) can sacrifice one rolled damage die to boost the attack total before comparing against AC/DC. The die is still rolled, but its value is added to the hit check and not to damage.

Guiding Bolt (4 d6): Caster rolls ability dice + proficiency + 4 d6. They may declare 1d6 a Risk Die to all‑but‑guarantee the hit, leaving 3 d6 for damage.

This lets casters lean into reliability at a real, visible cost.

4. Advantage & Disadvantage

Instead of rerolling everything:

• Advantage: add one extra d4, then drop the lowest result.
• Disadvantage: add one extra d4, then drop the highest.

Stacks add one die for each level of advantage/disadvantage; when both are present, process them left‑to‑right, adding dice first and then dropping the appropriate number of highs or lows.

5. Saving Throws & Opposed Checks

The attacker (or spellcaster) rolls their full pool (using Risk Dice as desired) to set the DC. Each target rolls a pool based on the stated save (e.g., Dex save ⇒ Dex modifier ± proficiency). Meet or beat the DC to shrug off or halve the effect.

6. A Dice‑Budget Action Economy

At the start of your turn you receive your full pool of d4s. Each action you take consumes one d4 from future rolls this round:

Action, Dice available
1st, Full pool
2nd, -1 die
3rd, -2 dice
Reaction(s) continue counting down

When you would roll zero dice, you’re out of actions until your next turn. This organically rewards higher‑level heroes (bigger pools) with extra swings, shoves, or spells while dropping the bookkeeping of bonus‑action minutiae.

7. Spells & Powers as Dice‑Cost Abilities

Give each spell a minimum dice threshold—effectively its “level.” Casting Fireball might require 6 dice; once cast, it also subtracts 6 dice from what you have left this round. Low‑cost cantrips remain flexible; high‑tier magic demands commitment.

8. Design Goals & Early Observations

1. Bell curve consistency. More dice tighten results around the mean, so mastery shows up as reliability, not just higher ceilings.

2. Unified roll. Attack & damage merge, speeding combat by ~30 %. Glancing blows feel better than total misses.

3. Transparent risk‑reward. Risk Dice give casters agency every time they sling a spell.

4. Fluid turns. The dice‑budget action economy lets players decide whether to flurry or conserve without extra keywords.

Probability snapshots (simulated):

• 5 d4 averages 12.5; 5 d4 + d8 averages 17.5.
• 8 d4 swings between 8‑32 but 50 % of rolls land 14‑19.

9. Next Steps

• Playtest! Start at 3rd level, log how often attacks hit vs RAW.
• Tweak armor baselines. AC 18 may feel too spongy at low dice counts.
• Edge cases. Critical hits, resistance/vulnerability, and area effects need firm wording.