Why I love PBTA’s 2d6 dice system and how the math works so well.
Written by: Trip
Every TTRPG has their own system for determining the effectiveness of player actions, and most of the time this is achieved through the use of dice. But which dice you use can shape the system and the type of play it encourages. Some use D20s, others use D6s. Some games want you to roll above a certain number, others prioritize low numbers (usually when trying to roll below a character’s attribute/skill score.)
But rather than List every single possible system that could be used to simulate random chance like some kind of proverbial fleet of infinite monkeys typing on infinite typewriters, I’m just going to talk about one of my favorite dice systems, Powered By The Apocalypse (or PBTA, for short.)
Let’s start with the basics. PBTA is a base 2d6 system. Everytime you want to do something, you roll 2d6. Certain circumstances can give you advantage or disadvantage on the roll (which have different names in different PBTA games. In Monster of the Week it’s called “Hope” for advantage and “Despair” for disadvantage) in which case you will instead roll 3d6 and take the highest two or lowest two, respectively.
But what numbers are you trying to get? Unlike D&D where every action can have a different DC you need to hit to succeed, each action in PBTA has exactly 3 possible outcomes with fixed ranges for those results.
- 10+ = Critical Success. You get the best possible outcome.
- 7-9 = Partial Success. You did what you were trying to do, but there might be some kind of complication, such as having reduced effect, expending additional resources, or taking damage from the attempt.
- 6- = Failure. You don’t get what you want, and usually end up paying a price for the attempt.
As most of you probably know, the most-common number to roll with 2d6 is a 7, meaning that most of the time you’ll be getting a Partial Success, with the occasional 10+ and 6- from time to time.
But the best part of the design comes when you factor in Stat Bonuses.
In PBTA games, PCs have 5 Stats which vary from game to game. Each Stat gives a bonus to certain actions ranging from +3 to -1. Most characters start with a Stat Array on +2, +2, +1, +0, -1. Whenever you gain a level, you’ll get to pick between about 7-10 different options, and usually about 2 of them allow you to increase a Stat by 1.
Those of you who are mathematically inclined may be starting to see the beauty of this system already. With an average roll of 7, a +3 turns your average from a 9 (Partial Success) to a 10 (Critical Success.) and conversely, a -1 in a Stat means your average roll will be a Failure. So it’s extremely preferable to both increase your Primary Stat to a +3, as well as boosting your dump Stat to +0. And of course Stat increases aren’t the only options available to you when you level up. Most Players will probably want to take additional Moves (the equivalent of Feats in D&D) rather than just increasing a Stat. Some characters also have narrative-focused Boons to choose when leveling up, such as gaining new companions or even changing their Playbook (basically their Class) altogether.
In conclusion, the dice mechanics of PBTA may seem simple on the surface, and they are. But beneath that simplicity lies a beautiful equation that shows that the designers absolutely know what they were doing.
About the Author:
My name is Trip and game design is my passion. I started out with D&D about 10 years ago, but have played a few other systems like Fellowship and Monster of the Week. I’ve even tried my hand at designing my own TTRPG a few times (maybe one of these days I’ll actually finish one?) I love both playing and running games, but I also love the oft-overlooked joy of learning new game systems. It always sparks my imagination seeing a new take on mechanics and rules, and I’m always excited to test the boundaries of those rules to see if they work as-intended and whether they can be improved upon. And who knows? Maybe someday I’ll successfully create my own game and become a household name in the TTRPG sphere? A boy can dream. 😅
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