Dice pool mechanics is our guilty pleasure here, right? Here is an idea which I need to get out of my head.

The base case: You throw 4d6 and count all 1s and 2s as "fails". Zero fails means you succeed. One fail means you succeed at a cost. Two or more fails means you don't achieve the intended effect.

So there is three possible outcomes just like in the 2d6-7to9 mechanics well known from PbtA games. There is no single target number.

Rolling four d6 feels satisfying to me from a haptic point of view. I'm explicitly trying to get away from a d20-single-dice mechanic. More dice, more fun.

Counting ⚀ and ⚁ is easy and quick. No need to add any numbers.

So far, so good. The downside is the lack of nuance which a d20-target change from 13 to 14 provides. There are only two ways to make success more or less likely: Use more or less dice. Count more or less results as fails.

I like this idea from Index Card RPG of having a target number per scene and everybody always rolls against this target. Keeps the pace quick. For this aspect, I would use the number of dice. So within a scene, players will always roll three, four, or five d6. Three is the easy "sun is shining" scene. Five is the hard "snowstorm and earthquake" scene.

Within a scene, the characters can do "easy" or "hard" actions. In the easy case, only 1s count as fails. In the hard case, even 3s count as fails.

I considered doing it the other way round, but counting different numbers is easier to correct. The action difficulty changes more often than the scene difficulty, so it is easier to get confused about it. If a player gets confused about the action difficulty and they roll the wrong number of dice, they need to roll again. If they count the wrong faces, they can quickly recount. Easier to correct.

Now the probabilities:

       | Success | At Cost | Fail |
Easy   |     48% |     39% |  13% |
Normal |     20% |     40% |  40% |
Hard   |      6% |     25% |  69% |

So in an average scene a hard action will fail with a 69% chance. However, with an easy action, there is a 48% chance of a clean success.

With 5d6 "snowstorm and earthquake":

       | Success | At Cost | Fail |
Easy   |     40% |     40% |  20% |
Normal |     13% |     32% |  54% |
Hard   |      3% |     15% |  81% |

The hard action failure chance has now increased to 81%. The easy action success has decreased to 40%.

With 3d6 "sun is shining":

       | Success | At Cost | Fail |
Easy   |     57% |     35% |   7% |
Normal |     30% |     44% |  26% |
Hard   |     13% |     38% |  50% |

Here a hard action will only fail in 50% of the cases. An easy action smoothly succeeds with a 57% chance.

In theory, you could add or remove even more dice but this is probably a strong enough effect already. It should have a nice chilling effect, when the GM announces "this is hard, add a die to your pool" and now there is one more of those dreaded fail opportunities.

I used this anydice to calculate the probabilities.

So what do you think? I consider it a mix of the PbtA-2d6 outcomes together with Fate-Fudge-like counting. I don't know of any other system which uses a mechanism like that but I would be interested if there is something similar already out there?