I’m working on a game concept, and I want a four-way resolution mechanic that comes close to Apocalypse World RPG roll probabilities (including “12+” critical successes), but that uses a dice pool.
Apocalypse Dice
Roll 2d6. Outcomes are interpreted as follows:
12+ = Critical Success. 10+ = Success. 7-9 = Mixed success. 6- = Failure.
(The above is modeled on anydice.com with the formula: output 2d6.)
Fate Dice
Fate RPG was the first dice pool I tested. Roll four dice. Each die has an even chance of turning up a +1, 0, or -1. Add up all the dice, giving an outcome of +4 to -4.
(The above is modeled on anydice.com with the formula: output 4d{-1,0,1}.)
I’m using Fate dice “by the book” — bonuses are added arithmetically to the 4dF sum. Adding more Fate dice wouldn’t improve the player’s chances anyway, it would just widen the curve, pushing more results into both Successes and Failures.
Can Fate Mimic Apocalypse Rolls?
Mimicking a straight Apocalypse roll (+0 bonus) with Fate dice:
- Success on a +2 or better
- Mixed success on a 0 or +1
- Failure on a -1 or below
I used a combination of a spreadsheet and AnyDice.com to come up with the following data:
Not bad. You can see that in Fate, your chance of failure is a lot lower (10-12 points) with a bonus, somewhat higher (3-10 points) with a penalty. Mixed results don’t come up much when the modifier magnitude is high in either direction. And successes are much more common (12-25 percentage points!) with any bonus at all.
I tried shifting the Fate line to the right by 1, but the match-up was even worse. This is the best Apocalypse impression that Fate can do.
Fate is not really a proper dice pool mechanic anyway, because the size of the pool never changes.
Can The Pool Mimic Apocalypse Rolls?
In The Pool RPG, you roll a handful of d6s. If you roll any 6s, you succeed. I’m tweaking that a bit: one 6 is a Mixed Result, two 6s are a Success, and three or more 6s are a critical success (what I’ve called a “Super Success” in my charts).
I set the standard roll at 4 dice, equal to a +0 in PbtA. Bonuses and penalties add and subtract dice from the pool, which is how a “dice pool” mechanic is supposed to work.
How does The Pool stack up?
The Mixed Result probabilities track very closely! But the chance of failure is much higher with positive bonuses than in PbtA. Which gives me an idea…
Double Pool!
What if, whenever you add a die above 4 dice, you add 2 dice instead? So your pool size, with bonuses, goes: 1, 2, 3, 4, 6, 8, 10, 12…
(And let’s look at the Super Success chart while we’re at it:)
Double Pool stacks up really well! The chance of failure is slightly higher (5-8 points) for positive modifiers; otherwise very close tracking. But the system is a bit klugey, with the “above 4 dice, add 2 dice at a time” thing.
Can Blades in the Dark Mimic Apocalpyse Rolls?
I should have tested Blades first, considering it was derived from Apocalypse World. In BitD, you roll a handful of d6s and look for the highest number. If it’s a 6, that’s an unmitigated Success. If it’s a 4 or 5, that’s a Mixed Success. If all you have are 1-3s, that’s a Failure. A critical success is 2 or more 6s.
Let’s say a straight roll (+0 in PbtA) is 2 dice in BitD. Here are the probabilities. I’m getting tired of copy-and-pasting, so here’s all four charts at once:
The Mixed Result probabilities track VERY well. But the chance of failure is much lower across the board with BitD dice. Unexpected, considering Blades is a dark and gritty game AND it contains other mechanics to mitigate bad rolls.
Can “5s n’ 6s” Mimic Apocalypse Rolls??
Alright this is something I just made up (although I feel like I’ve seen it somewhere before). Roll a pool of d6s. 5s and 6s are hits. No hits is a Failure, 1 hit is a Mixed Result, 2 hits is a Clean Success, 3 or more hits is a Critical Success.
I set the straight roll at 2 dice. One penalty brings you down to 1 die. For a “zero dice” roll (2 penalties), roll 2 dice and keep the lower. For “-1 dice” (3 penalties), roll 3 dice and keep the lowest.
Pretty good! Successes and Mixed Results track very well outside of negative modifiers. With 2 or more penalties, the chance of Failure is much higher. And the chances of Super Successes is significantly lower overall. But altogether a serviceable replacement for 2d6.
Here is, as they say, everything all at once:
We can see that Fate and The Pool are really outliers compared to the rest. Fate makes you feel like a hero. In The Pool, failure is always one step away.
P.S.: d10s, Man
My friend Paul suggested this one after I originally published this post. It’s a very interesting mechanic!
Roll a pool of d10’s. Look at your highest result.
- On a 7 or lower, it’s a failure.
- On an 8 or 9, it’s a partial success.
- On a 10, it’s a full success.
Take 3d10 as your straight “+0” roll. You can read Paul’s detailed analysis of this system here:
https://gauntlet-archive.github.io/t/pbta-mechanics-with-d10s-improved-ladder/6292.html
Here’s how it compares to the Apocalypse:
Successes are a bit more generous until you get above +2, where they level out. Beyond +2, success probability doesn’t rise as steeply. As Paul says, “more resolution” up at the high end.
Mixed Results and Failures track very well indeed.
The chances of Critical Successes are vanishingly small.
P.P.S.: I added one tweak to Paul’s d10s roll. A Critical Success is a 10 plus either a 9 or a 10. This gives a nice fat Crit curve, a little more generous than standard PbtA and the other favourite mechanics on here.
Outside The Red Box 