Saturday, February 27, 2021

A Simple 2d6 Skill System

Jorune: Evolutions uses a stat and skill check system that is different than the mechanics used in combat. Since Jorune: Evolutions is OD&D inspired, in another post I tried out a unified mechanic that employs the 1d6 that OD&D uses for most things. It was simple and the math was very transparent in a player-facing way. It also had a certain cleanness to it in that progression is linear and even a +1 opens up the ability to meet challenge levels that were previously closed. 

A possible downside is that it makes those low modifiers very significant, especially when it comes to opposed rolls where having an advantage can lead to stacked modifiers. This would have been OK, except for the fact that I'm using opposed rolls for grappling in unarmed combat and giving a +1 modifier for being large sized. (My next post will explain.) This would have resulted in each group having at least one unarmed boccord specialist in it, i.e. a half-giant professional wrestler. That game sounds amazing, but it's not the game I'm trying to design. 

The other possibility, with which I originally started, was to use a 2d6 system. This fits with the reaction roll mechanic and downtime system I'm using. Also, as Alistair mentioned in the comments on the 1d6 skills post, classic Traveller used a (janky) 2d6 skill system, so it has a nice pedigree for old school sci-fi gaming. That it picks up the PbtA resonance is a welcome result for me, and Cepheus system games use it as well. If you put a chart--like the one below--that shows the probabilities of success as a percentage chance on the character sheet, then you can make the math transparent enough to the players I hope. And as Tom Killion mentioned, it's fun and more dramatic feeling to roll more dice than one. 

Types of Checks

There are four kinds of stat and skill checks in Jorune Evolutions. A roll can be opposed or unopposed. Each of these kinds of rolls can be a straight roll or a mixed roll. The Sholari will tell the player which of these types the roll is, and what modifiers will apply, before the player decides to roll the dice. 

Unopposed checks are tests against the PC’s skills or stats where the only opposition are the circumstances of action, inanimate objects, or natural forces. Opposed checks are made when the PC is attempting something that is resisted by another sentient being.

Straight rolls are rolls with binary results: success or failure. (Almost all rolls in classic D&D are straight rolls, with the exception of reaction rolls.) Mixed rolls are made in circumstances where the effect of success is uncertain and feels narratively like it should be a scale of possible outcomes. Since Jorune Evolutions takes inspiration from classic D&D, straight rolls are the default.  

Unopposed Checks

Roll 2d6 + stat or skill modifier + difficulty modifier. (Note: it is always a stat OR a skill check. The modifiers do not stack.)

Results (Straight): 6- failure 7+ success

Results (Mixed): 6- failure 7-9 mixed result 10+ Success

Stat Modifiers

-1 Sub-par

0  Average

+1 Excellent

+2 Supreme (You can only reach this level through big ticket sandbox advancement)

Skill Modifiers

-1 Untrained
0  Trained
+1 Skilled
+2 Master

Difficulty Modifiers

+1 Easy                   
0   Moderate           
-1 Challenging       
-2 Hard                  
-3 Severe               
-4 Heroic
-5 Epic               

Automatic Failure Rule

A penalty of -4 or worse is an automatic failure. This caps absurd attempted rolls. 

The Math

The following chart shows the probability of making a straight check (7+) conditional on the difficulty and your stat or skill modifier. To see the probability of getting a success on a mixed roll (10+) simply move down 3 rows. (At the difficulty rating of severe and higher it is not possible to roll a 10+.)

Opposed Checks

To make an opposed check, each party roll 2d6 + advantage modifier + stat or skill modifier. The advantage modifier is applied only to the party whose situation is more advantageous. In a straight opposed roll, whoever gets the higher total number prevails. In a mixed roll, consult the winner’s roll to see whether it is a mixed result or a success. A tie always results in a temporary stalemate. (Check again next round.)

Opposed Checks: Each party rolls 2d6 + stat or skill modifier + advantage modifier

Results (Straight): Whoever’s results are higher prevails.

Results (Mixed): Whoever’s results are higher prevails. Consult the winner’s result: 9- mixed result 10+ Success

Advantage Modifiers

+2 Great Advantage 

+1 Advantage

Automatic Victory Rule

If the difference between the modifiers of the two sides is 4 or greater, the side with the higher modifier automatically wins. 

The Math

Let's consider the chance of winning for a PC based on the difference in modifier with their opponent. So start with their total modifier and subtract the opponent's total modifier from it. The result will range from +3 to -3. For example, if a PC has excellent strength (+1) and advantage (+1) and their opponent has subpar strength (-1) we get 1+1-(-1)= +3. Keep in mind that there is also the possibility of ties, so this doesn't measure your chance of losing, only your chance of winning:

+3 = 76%
+2 = 66%
+1 = 56%
0   = 44%
-1 = 34%
-2 = 24%
-3 = 16%


  1. Thanks for posting. This is extremely close to to the Fighting Fantasy system (Advanced Fighting Fantasy, too). Are you familiar with it? The only difference in mechanics is that unopposed checks are roll-under in FF. Of course, FF is related to Traveler (and T&T).

    1. I am familiar with it. I read the originals when I was a tween, and I read the more recent reboot a couple of years ago. I didn't have them in mind when writing this, but you're right of course. Thanks for that. One big difference is that AFF has a much higher stat range, both in starting scores (with the point buy system) and in the scores of advanced characters. As a result, the roll under the stat makes stats very important. My system hews closer to the pre-supplement I OD&D where stats were (generally) tightly constrained and less important. Also, AFF has skill modifiers stack on top of ability modifiers, whereas in my system they never do, but rather are a separate track. You EITHER make a stat or a skill check.

    2. We're on the same wavelength. My home rules, which grow off the same tree, are similar to yours in having a smaller scale of stats and having one stacker rather than two. I hope your play-testing goes well, and happy gaming!

  2. Looks a bit like the "Powered by the apocalypse" core roll, with its threefold instead of binary outcome.

    The miniature wargame Rogue Planet also uses 2D6, but caps the modifiers at -3 to +3 (as in: you simply stop counting once you reach these limits; everything included, stat-based, skill-based and situational modifiers). I think that makes a lot of sense. Certainly the 5 & 6 modifiers don't really add anything. And capping at 3 leaves a decent chance of failure even for the most skilled, as should be the case. Only roll when there's a genuine risk.

    1. Yes, the mixed result roll is intended to capture PbtA style rolls. (Although PbtA was itself using the reaction roll from early D&D.)

      For unopposed rolls this system caps the bonuses at +2, and that only for advanced characters, with a further +1 possible for easy tasks. So +3 max, but very rare, just as you say. I let negative penalties range much higher because that's fun, e.g. when players need to do something REALLY hard under pressure that even someone skilled is likely to fail at. I don't see a problem there.

      For opposed rolls maybe I let it get a little high, since one side could get up to +5 in theory, while the other side had -1. (I.e. Conan the barbarian arm wrestling Woody Allen on muscle relaxers). Probably under those circumstances you should instead just say: Conan wins. (As a DM I certainly would do that in play.) Maybe the categories should Advantage +1 and Great Advantage +2, that would let the mod go up to a max of +4. I think I'll change that now.

    2. I just adopted some of your suggestions, since they seemed good to me. On unopposed rolls a -4 or greater is now an auto fail, and in opposed rolls, comparative advantage is capped at +2.

    3. ...And I just did the same for opposed rolls. Capped at a 3 point difference. I now have adopted the Rogue Planet system, which I didn't know about before now. Thank you! I'm much happier with it.