About Me

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Seattle, Washington, United States
I'm an old time roleplayer who became a soldier who became a veteran who became a developer who became a dba who became a manager who never gave up his dream of a better world. Even if I have to create it myself.

Tuesday, February 11, 2014

Stellar Mechanics

photo credit: mag3737 via photopin cc

One of the lessons I've learned in the past few years is that I needed to figure out mechanics after I figure out the outcomes.

For Stellar, I need to get a core mechanic going so that I can explore the rest of the rules. But in the classic chicken vs egg fashion, I need some idea of the rules before I can select a trial mechanic.

d%? Not this time.

I mentioned before that I started with percentile dice. That proved unsatisfying.

When players roll most attacks/checks, my personal philosophy is they should end up succeeding more often than not. This sidesteps a common cause of frustration and helps avoid battles that go on too long.

To do that with percentile dice, I basically had to up the odds quite a bit, which produced two cascading issues of note:

  • Not much space for bonuses or level improvements, unless I apply a lot of compensating penalties at higher levels, which I don't care for. Subtraction slows down play enough with a d20, now put a d100 in that mix.
  • I tend to prefer single-roll resolutions. It's one of the things I really liked with Phoenix. Sure, there are games that play tricks with d% rolls. For instance, the tens digit might mean damage, the ones digit is location. Stuff like that. And that's ok, but doesn't feel as streamlined as I want.

Figuring out the Odds

After realizing I was heading down the wrong path (again?), I stopped and took a step back. I always had this idea of d% being the "perfect sci-fi" roll, but it clearly didn't line up with my expectations.

So I got pencil and paper and doodled a bit.

In the midst of the completely non-artistic scribbles, I drew two probability curves. One represented the odds of a PC hitting a generic bad guy, and another of the generic bad guy hitting the PC.

Others may support different philosophies (about many things), but for me, there's no problem with bad guys having different chances than PCs. Part of the cinematic fun in Stellar will be letting the PCs obliterate 20 enemies, instead of always feeling threatened by equal numbers. How many cylons could a main-character's viper take out? Yea. Like that.

Yep. That drawing class is really paying off.
Translation to "human" follows below.

My curves for bad guys hitting PCs came out something like:
  • Hits PC around 40% of the time
  • Crits PC around 5% of the time
  • Misses about 60% of the time

And for PCs hitting bad guys:
  • Hits bad guy around 70% of the time
  • Crits bad guy around 10% of the time
  • Misses bad guy around 30% of the time

They don't add up to 100% because Crits are also Hits. What does a Crit mean? No idea yet, but usually it involves either extra damage, or disabling part of the opponent.


As many of you have no doubt noticed, I really love this tool. With it, I can quickly explore large variations in base mechanics and find what fits my desired outcomes.

Here's the link to what I came up with: http://anydice.com/program/3462

Or basically,

output 2d[count {10..12} in d12]
output 4d[count {10..12} in d12]

Which is AnyDice speak for using d12 dice pools, and counting successes for each die that comes up as 10, 11, or 12.

With a bad guy using 2d, and a PC using 4d, it pretty much exactly fits the curve I was looking for (if you assume that "one success" is a hit, and "multiple successes" is a crit).

Immediately, story ideas form in my head to support this approach. For instance, it seems very plausible to me that the average X-wing is a little more badass than the average tie-fighter, both in pilot skill and in weaponry.

The overachiever math students out there probably notice that 10-12 on a d12 is the same as 4 on a d4. So why a d12? Simple: granularity. I want room to play with bonuses. I can give a small bonus like 9's count as successes for a certain roll, whereas on a d4 making 3's count is a huge bonus.

Also, d12s are more fun to roll and have caused fewer unarmored foot injuries over the years.

I'm not thoroughly attached to this mechanic yet. Now that I have a working theory, I'll apply it to some rules in the setting and see what happens when I play it out.


  1. Welcome back to what I hope are more regular posts.

    I'm enjoying reading about your insights into game design, mostly because I can't even start to think the way you seem to.

    1. Thanks... hope you are enjoying the summer! Rarely gets above 0 C here right now... most of the last month was -15 C or worse...

    2. Almost every day above 40C the last 3 weeks.


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