Dicing With Doubles
It has taken me a while to work up the nerve to post something to this blog, and no-one even knows it exists yet. Imposter syndrome is weird. Starting a blog as a newbie to the OSR feels a bit like walking into a party that started 50 years ago and trying to find a place to hang your coat.
So, maybe a lot of what I'm about to write is old news to you. But I've noticed something cool during my first forays into the world of X-in-6 chances and reaction rolls, so I'm gonna post about it. With any luck, it might spark an idea for your own game.
In Praise of the 2d6
Ah, the workhorse of the OSR world. The trusty old mule that'll never let you down. Countless systems put the 2d6 roll to work, for countless purposes, thanks to its defining characteristic: ✨the bell curve✨.
I hardly need to re-write the book on how useful a bell curve of probabilities can be as a designer. Extreme outcomes are rare. Mild outcomes are common. It's classic! You only need to look at how often it pops up in the most popular systems: weather rolls, reaction rolls, encounter tables, you name it. 2d6 rules. This isn't breaking news.
And yet, the bell curve is but one aspect of the humble 2d6's supremacy. What if there was another layer of goodness to rolling a pair of six-siders, which you can leverage with basically no effort?
Doubles!
Every 2d6 roll comes with the chance of rolling the same number on both rocks. Sounds obvious, but there are some cool characteristics to the probabilities of rolling doubles:
- The chance of rolling any double is exactly 1-in-6. The ever-present "it ain't likely, but it's likely enough to be worth rolling for" chance can also be modelled with doubles on a 2d6. Noice!
- Rolling either double 1s or double 2s has a 1-in-18 chance, or a touch more likely than rolling a nat 1 on a twenty-sider. So you can also model the next classic checkpoint along the "let's see if I really fuck up" road. Also noice!
- By the same token, double 5s or double 6s are almost equivalent to rolling a nat 20... sweeeeet!
So, now you can crit fail and crit succeed on a 2d6 roll, and by monkeying with which doubles mean what, you can dial in the feel of a system.
For example, let's say double 1s, 2s, or 3s are a crit fail (1-in-12 chance). Double 4s, 5s, and 6s are a crit success. Now, you have a 1-in-6 chance of a crit being rolled, but which way does it fall? Drama!
Maybe you want something similar to that occasional excitement of rolling a crit on a d20, so you assign crit fails to double 1s and 2s, and crit successes on double 5s and 6s. There's a 1-in-9 chance of rolling one of these. Perhaps useful for special encounters on a wandering monsters table—rare but not unheard of.
If you want to introduce really extreme outcomes, double 1s and double 6s each have a 1-in-36 chance. These could trigger supernatural conditions on a weather table, or indicate vast treasure hoards during dungeon stocking.
Upping the Stakes
By developing the idea a bit further, the doubles layer can support the fantasy of certain in-world activities.
Consider a simple downtime system for gambling, where the player rolls 2d6 for each night spent at a casino to see how well they do. Rolling low loses coin, rolling average breaks even, rolling high wins some coin. It's simple, but lacks drama. Let's add some.
Roll double 1s and you end up in serious debt with a bad sort. Roll double 6s and you land the jackpot!
Now we're talking. There might only be a 1-in-18 chance of one of these outcomes occurring, but just the possibility will add tension and fun to the roll. Can we push it further?
Each subsequent night of gambling raises the stakes:
Night One: No chance of disaster or jackpot.
Night Two: Disaster on double 1s. Jackpot on double 6s
Night Three: Disaster on double 1s and 2s. Jackpot on double 5s and 6s.
Night Four: Disaster on double 1s, 2s, and 3s. Jackpot on double 4s, 5s, and 6s.
Oh yeah. This is starting to feel like a Thief who doesn't know what's good for them. The system allows them to push their luck—the stakes increasing with every attempt. Roll again for a better chance at the jackpot, but an equal chance of getting your legs broke by the mafia! By night four, there's a 1-in-6 chance of an extreme outcome.
This is all while maintaining the "base layer" of the 2d6 distribution for non-double results. The trusty ole workhorse is plodding along dependably in the majority of cases. The doubles system is building on the shoulders of a giant—not so conspicuous that it steals the spotlight, but enough to give the system some feel and portray the fantasy of the activity.
Further, like natural 1s and 20s on a twenty-sider, the doubles system is resilient to modifiers. You could add a "hot-streak" modifier that increases with each successful night, and adds a bonus to the next 2d6 roll. The increased chance of winning some cash might convince the gambling PC to push their luck, but the chance of rolling disastrous doubles are just as likely, modifier or no!
Make Doubles Matter
The doubles layer is a freebie, every time you roll a 2d6. Take your favourite 2d6-based resolution mechanic. How might you spice it up by making doubles matter? Some additional ideas:
- Encounter Tables: Special or sequential encounters trigger on doubles. Start on 1s, and introduce other doubles after PCs spend a certain amount of time in a location.
- Weather Tables: I bet you already have ideas about what happens on double 1s. Other doubles might be beneficial or even magical environmental effects.
- Reaction Rolls: Double 1s or 2s? Not only do they attack, they fight to the death! Double 5s or 6s? You have a new adoring fan.
I'm especially interested in how this could be applied to a downtime system such as Elmcat's. Doubles make great opportunities to introduce further complications or roadblocks to a downtime activity, and I bet it could be worked nicely into the system as a whole. More on that if I figure it out.
Until then, make doubles matter!