# Dice Pool Rationale

This archive page preserves the reasoning behind the shift from the traditional d20 system to a d4 dice pool mechanic.

## Why Not d20?

The **d20 Test** system (used in D&D 5e) is simple and widely recognized, but suffers from:

- **High variance**: Every number from 1 to 20 is equally likely.
- **Poor skill reflection**: A highly skilled character can still roll a 1 and fail, while a novice can roll a 20 and succeed.
- **All-or-nothing feel**: Pass/fail results flatten tactical depth.

## Why d4 Dice Pools?

The d4 pool system emerged from a desire to:

- Reduce swinginess through bell-curve probability
- Make character building choices feel **consistently impactful**
- Naturally scale with character growth

### Core Concept

If we were to simply change from using a single D20 to using a number of D4s we could roll a number of **D4s** equal to:

- **Attribute modifier**  
- Plus **Proficiency bonus** (if applicable)

You sum the results. For attacks or spells, include the weapon or spell’s **damage die** in the roll.

Then:

- Subtract target’s **Evasion or DC**
- The remainder is damage (or effect strength)

<WRAP></WRAP>

> Example:  
> A fighter with +3 STR and +2 Proficiency uses a longsword (d8).  
> They roll **5d4 + 1d8**, subtract the target’s Evasion, and apply any remaining value as damage.
> <WRAP notice>Note that the max roll of 5d4 is 20, simulating a D20 roll but with a smooth bell curve.</WRAP>

## Built-In Action Economy

By reducing your dice pool with each action, the system naturally limits multi-action abuse:

1. **Start of round**: Action Load = 0  
2. **Take action**: Add 1 to Action Load  
3. **Dice pool for next action** = Normal total dice − Action Load

<WRAP></WRAP>

> This replaces D&D’s Action/Bonus/Reaction system with something **more fluid but self-limiting**.

## Advantage / Disadvantage

Modeled as adding or removing d4s:

- **Advantage**: Add a d4, remove the *lowest* die rolled
- **Disadvantage**: Add a d4, remove the *highest* die rolled

Multiple stacks add/remove more dice. It’s a smooth mechanic that stacks intuitively.

## Risk Dice

For powerful effects (like spells with high damage), the player may:

- **Sacrifice one of the damage dice**
- Add it to the attack roll to boost success
- Omit it from damage if the spell hits

This creates **tactical tension**: ensure a hit, or go for full damage?

## Misses and Zero Pools

- If a player-initiated action would roll **0 or fewer dice**, it can’t be attempted.
- If the **GM calls for the roll**, the player always rolls **at least 1d4**—even with negative modifiers.

## Additional Notes

- High-tier abilities can require a **minimum pool** (e.g., "Fireball needs 6 dice to cast")
- Dice serve both as **resolution** and **resource tracking**
- Everything stays visible and tactile—no hidden math

## Tools

- Probability modeling: <https://anydice.com/program/3c172>

## Why Not D6 Pools?

At first glance, using a pool of D6s might seem better than a pool of D4s. The variance is greater while still being a solid bell curve of probability. But there are a few problems.

The first is that when rolling D6s it is harder to easily total the results. Using D4s leads to [most rolls are mostly pairs adding to 5](rules:sidebar_d4_math), making addition quick and easy. That isn't true with D6 pools.

The second is that the variance between low-skilled and high-skilled characters is too vast. Trying to determine the number of dice to roll matches up pretty well with D4s but not D6s. An example might clarify.

<WRAP important>
Compare the min and max possible rolls of two different pool sizes, related to their Attribute Modifier.

| # of Die | D4 Min | D4 Max | D6 Min | D6 Max |
| --- | --- | --- | --- | --- |
| 2 | 2 | 8 | 2 | 12 |
| 5 | 5 | 20 | 5 | 30 |

You can see that when using D4s it more closely resembles the results when using a single D20. The maximum a skilled character can roll is in line with what we'd expect. But the max result for a skilled character when using D6s is much higher than we'd expect.
</WRAP>

So this means we would either need to create a different method of figuring out how many dice to roll, or expand the way we calculate success/failure. Doing the latter adds the problem of converting from standard D&D sources.

But by staying with a D4 pool we can easily calculate the number of dice while making translations from D&D sources a breeze.