An Alternative Dice System for D&D Next

This article previously appeared at the Hobbit-Hole.

One of the many things I love about D&D Next are the Skill Dice and Expertise Dice (I much prefer this name to Martial Damage Dice). They give the game extra tactical and tactile dimensions. That actions involve more dice rolling is a great direction for the game.

The basis for action resolution (DC, AC) is still the venerable d20 + static bonus. Inveterate tinkerer that I am, I couldn’t help but imagine what other dice systems could be used and what their effect might be.

Chris Sims’ 3d6

Chris Sims, one of the 4e designers, posted in a blog entry that his group uses 3d6 rather than a d20 during combat. (Sadly that blog entry on Loremaster.org is no longer available due to a crash.)

3d6 generates numbers on a bell curve. All other bonuses being equal, the net effect is to increase the hit rate from about 60% to 75%. This makes combat go faster and players got to use their cool powers more often.

What about the natural 20 critical? Well, Mr. Sims simply calculated that since natural 20 is a 5% probability, 16+ on 3d6 is also about 5%, so any roll of 16+ was a critical.

The substitution is easy and straightforward. All other rolls continue to use d20.

Dice Pool for D&D?

Our antics with dice don’t have to end there though. What about the other checks? Can we make those more exciting than a simple d20 + modifier?

Since we love to roll dice, let’s use a dice pool. The more effective you are with a skill or weapon, the more dice you roll.

An ideal change would have to be roughly the same probability. We don’t want to send things too far off the beaten track. If at all possible, we want to keep all other factors (i.e., DC, AC, HP, etc.) the same, or at the very least easily adjustable to compensate.

Base Dice

Just as with Mr. Sims, we will replace the d20 with 3d6. This gives us a good approximation of the d20 range but focuses the numbers on 9–12. This will make medium DCs easier to achieve, whereas higher DCs will be more difficult.

Bonus Dice

Normally a static bonus concocted from ability score, level, skills, etc. is added to find the total result. Since we are forming a dice pool, let’s replace the static bonus with dice!

The list below shows each static bonus and the bonus die roll to substitute. Each is linked to a chart on anydice.com that shows the probabilities of the dice pool roll to be compared to the static bonus roll. I’ve only included through +10; hopefully the progression should be evident for higher bonuses.

To determine which bonus dice to use, I compared what number would be rolled at least 50% of the time on a d20 roll and approximated the same percentage equivalent for the dice pool roll. In most cases, the numbers that would be rolled 50% of the time were +1 to +2 higher than the d20+bonus roll (e.g., on a d20+1, 12 or higher will be rolled 50% of the time; for 3d6+d4, 13.5 or higher will be rolled 50% of the time).

These are fairly straight forward substitutions and maintain roughly equal probability distributions. If you are truly concerned about maintaining parity, you could simply add +2 to all DC/AC rolls and be close enough for government work. I prefer allowing my players to succeed a little more often. (Remember, monsters will succeed more often too.)

Since the goal was to keep the probabilities roughly equal, the progression stutters since it doesn’t map perfectly. In some cases I opted to increase the minimum roll rather than the maximum by using a higher combination of smaller die, such as +3 = d8, +4 = 2d4.

Exploding Die

In a normal check, a 20 is a thrilling result and usually elicits cheers. Depending on how many dice you roll in a given session, a 20 probably happens once every session or two. Since we are rolling dice on a bell curve, the maximum results occur far less often (an 18 on 3d6 occurs ~0.5% of the time). What if we could add something that would generate the same excitement to our dice pool? Ladies and gentlemen, I give you the exploding die[1].

For those who aren’t familiar with the term, an exploding die is one that is rolled again and added to the result, usually when its maximum value is shown. For example, if an exploding d6 rolls a 6, it is rolled again and the second roll is added to the original 6. If the second roll is also a 6, the die is rolled again, ad infinitum.

In our playtest, a single exploding d6 from the base 3d6 seems to work best. We use a different color die to eliminate confusion about which die is exploding. The same drama is generated often enough, and we sometimes see spectacular results. In a tense moment last week, our wizard was being attacked by a gargoyle and used Shocking Grasp as a last ditch effort; he rolled a 6, 6, 6, 1 with the exploding die for a total of 35 on his check. Cheers around the table.

The difference in probabilities is negligible with the exploding die. Taking the charts above, let’s examine the +5 roll and see how that compares:

We can see that the probabilities go up slightly for each number. The increase for rolling a 10 is 0.4%; rolling an 18 is 4% more likely (less than a pip on a d20).

Criticals and Fumbles

As with the rest of this mechanic, keeping the frequency of criticals and fumbles is a goal. Since these happen 5% of the time on a d20, that’s our metric. Also, since the static bonuses aren’t taken into a account, neither is the bonus die; only the base 3d6 are used.

Using 3d6 with an exploding die, a 19+ occurs about 5% of the time. Since we are using an exploding die though, more dramatic totals are possible. We can use that to create some more dramatic effects: when the exploding die rolls a 6 more than once, damage is increased an additional multiple. For example, in the wizard’s roll above, the two extra rolls of 6 resulted in a 3x max damage multiplier.

Fumble probabilities are handled similarly. Since 6 or lower happens 5% of the time, any roll of 6 or lower on the base 3d6 is an automatic failure. While lower numbers could produce catastrophic failures, it’s not really feasible to create super negative rolls; a failure is a failure. You could use a fumble table, but I don’t.

Negative Modifiers

Just subtract the modifier from the 3d6 roll. Don’t roll the bonus die.

Advantage and Disadvantage

Just re-roll the entire roll.

Playtest

We’ve used this system for a few weeks, and it seems to work well. Most of our players enjoy it. Some don’t like it as much. Those who haven’t enjoyed it use the standard dice rule; we haven’t noticed a particular disparity in success for one system or the other. The DM is using it and likes it. He just jots the bonus dice down next to the monster/NPC attacks.

More Polyhedral Fun Next Time

There is more that can be done, but my word count is fast approaching has surpassed my self-imposed limit, so I will wait for my next article to address more thoughts on this subject. As a hint, think Warhammer FRP 3e.

What do you think? In particular, I would appreciate a more rigorous analysis; if it’s busted I would like to know about it. Contact me via e-mail or Twitter (@icosahedron)


  1. Well, I didn’t invent the exploding die concept, so I can’t give it to you. Lots of systems use exploding dice, perhaps most notably Savage Worlds.  ↩