METTLE Hybrid Dice Pool

There is a recent trend towards RPG designers leaving design notes in their actual game books. I have mostly avoided them in my work. If the reader cares they will find out soon enough through play, and if they do not it was probably unimportant. Perhaps the readers will make a video or write a blog post about the "unspoken design intent" or some such - why spoil their fun by explaining it before they do?

     In METTLE Core I had one lapse. Gaze upon this one shameless morsel of designer narcissism, from the Engine chapter:

Note: the average score of a single die is 1, making it easy to gauge chances of success. This also means you can directly contest single attributes, using one as the active check and the other as the passive difficulty.

     I like to think this was restrained, driven by the obvious necessity of explaining why I just didn't use a "normal" dice pool everyone is already familiar with. In this largely unread blog well outside of my similarly unread game books, I am less constrained by good taste and dignity.

     So let's dive deep into why I used a strange hybrid dice pool for METTLE!

Direct Contests

The biggest reason is that it allows you to directly Check a single Attribute against another, rolling one Attribute and using the other as the Difficulty. In METTLE they are equivalent! This may seem abstract but it really makes the design space much more flexible.

     The usual solution in other dice pool systems is opposed Checks or "Contests". Here both sides roll their die pool. This is also direct, but eats up time and patience for both the player and game master - especially if there are a lot of enemies or actions.

     Another typical solution is to set a defender's stat as the difficulty of a check, but with standard one die equals one success pools, the difficulty is too high! Most dice pool outcomes average out at about half of the pool or less. Other games that do this get around this with an indirect kludge: halve the defending pool or add an Attribute or Skill to the attacking pool. This pumps the number of dice up pretty high and the effect of the doubled or halved pool will scale oddly as numbers increase.

Margins/Edge

Most dice pool systems count the number of successes over the difficulty as a margin-of-success. In METTLE there is no subtraction, you just count your Edge (4-6 faces). Edge dice would normally just be failures (or worse, "scoundrels") in other dice pool systems, but here every die that falls is important. You want to roll 1-3s for a good Score, but you also want 4-6s for Edge!

Probabilities

The central conceit here is that the average score on any die is 1, ranging from 0 to 3. You can check this yourself: adding the Scoring faces and dividing by the total faces gives us:

 (1+2+3) / 6 = 1

     It's also a pretty minor feat in Anydice to check this: 

Mean/average is always the same as the number of dice, deviation increases reliably with dice, and the maximum is always 3x the pool. Really a lot of desirable behavior.

Origins

This traces back pretty far to a post on RPG.net back when you were allowed to argue about game mechanics on the game design section. Believe it or not, what is now a silent desert was once a thriving little ecosystem of horrible nerds.

https://forum.rpg.net/index.php?threads/d6-system-but-reading-the-dice-differently.782505/post-20113769

They did bring up a fair criticism that the modal value of the dice was a little odd at lower dice pools (<5), but this is also a reason I avoid using die penalties and raise Difficulty instead.

Conclusion

That's all for now. I'm probably not posting this widely because it is very niche as far as interest.

Pipe up if you have any comments. You know what to do.