BMDev 1: Behind the Attack Design

Small changes can solve complex problems

If you’re not sure what BMD is, check here:

BMD: A True Contender TTRPG

The BMD attack resolution system is one of the highest design priorities. The game is explicitly about guns-free open conflict. Thus, we need a reliable means to mediate that conflict in a way that is both satisfying and sound.

Attack/Defense has undergone significant iteration to get to its current state. Surprisingly severe early design difficulties led to a deep investigation that required treating multiple mechanisms as a unified system. This ultimately resulted in a clean, coherent design. Let’s examine the early iterations to see what went wrong and how things were resolved.

(Terminology has changed a lot through various design iterations and may change in future iterations. I always endeavor to use up-to-date terminology to reduce confusion.)

Building Blocks: Tests and D10s

Before we move to specific game mechanics, let’s get the fundamentals out of the way. The essential dice mechanic in BMD is the test—rolling a single D10 to hunt for a success, a result of 10 or more (10+).

A +3 bonus to a test shifts the distribution of results from 1-10 to 4-13. Rather than a single possible success outcome (10), a test with a +3 bonus has 4 possible success outcomes (13, 12, 11, 10).

A more simple way of seeing this is to ask what result is needed for a success. An unbonused D10 requires rolling 10 to get a success. A +3 bonus implies we need to roll a 7, 8, 9, or 10 to get a success. This is simplified to 7+ (rolling 7 or better). For reasonable values X, a bonus of X will require rolling 10−X or better.

Operationally, the game might demand that we count the successes from 9 tests. Let’s say the tests have a bonus of +2. We roll 9d10 and look for results of 8+ (10−2 = 8). We simply count the number of successes.

In this way, the focus is on counting (1-2-3-4… etc.) rather than arithmetic (e.g. 12 + 9).

Combat Resolution: Early Iteration

For clarity, figures (single individuals) have individual scores but operate only in units (cohesive collections of figures that act as one body).

A [Score] test is a test with a bonus equal to +[Score]. A figure with Accuracy 3 making an Accuracy test needs to roll 7+ (10−3) for a success.

Design Goals

Without clear goals, we’re left dreaming up and choosing between “valid” designs instead of zeroing in on the best design—the one that most successfully reaches our desired outcomes.

In this case, we have two design goals driving our consideration.

a) Ease of mental calculation.

I want players to spend their mental energy strategizing. The less their working memory is devoted towards resolution mechanics, the better. This is a game-wide consideration.

b) Players only need to know the precise scores of their own figures.

Everyone involved should only need to intimately know their own units. Many games have resolution mechanisms that require comparing an attacker’s score to a defender’s score to adjudicate a die roll—nothing wrong with that. But BMD at scale is a complex beast; there’s plenty to be thinking about. Trying to remember whether the thing you’re shooting at has X defense or X+1 defense is something I want to minimize—particularly because the thing you’re shooting at can change from round to round.