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Dice Mechanic Noodling: Hilo d6s

I had an idea for a little RPG dice mechanic recently, so I plugged it into Anydice to see what it looks like. (If you are interested in games, dice, or probabilities and you haven't checked out Anydice, I highly recommend it.) You can take a look at the program here.

The idea is to roll two six-sided dice and total them. If a die rolls 1 or 6, it explodes. However, 1s explode negatively while 6s explode positively. That is, if the die comes up 6, add it, roll it again, and add the second result to your total. If the die comes up 1, add it, but then roll it again and subtract the second result. The dice only explode once, so you get a final total between -10 and 24, inclusive.

What does this give us? Well, the graph looks like this:
Hilo d6 + d6
Weird, I know. It's a straight 2d6 pyramid in the middle, but with a bell curve on either side that tails off sharply at the extremes. The shape gives us some obvious zones of effect to work with, though.

The flat tails at either end are our obvious extreme cases (that is, from -10 to -4 and from 18 to 24). Call them extraordinary success or failure, criticals, whatever. These are the really good (or incredibly bad) outcomes that shouldn't happen very often. And they don't: only about 2% of the time for each.

From where the line ramps sharply up or down (-3 to 2 and 12 to 17), we have full failure or success. These zones are useful, if a little boring, and they hit around 17.6% of the time each.

It's the middle pyramid, from 3 to 11, that is the fun part. If the result falls in here, you can choose to succeed at some kind of cost. This is the 7-9 result from Apocalypse World, but it hits nearly half again as often: about 60.8% of the time.

For purely aesthetic reasons, I'm tempted to set whatever trait you add to the roll to an average value of 3. This gives the following results table:

Less than 0: Extraordinary Failure
0-5: Failure
6-14: Success with Cost
15-20: Success
21+: Extraordinary Success


I'm not sure where I might take this, but it was fun working it out. I can see it being used for games where the characters typically succeed, but with ever-escalating danger. Possibly something in the pulp area. If you like the rules and want to do something with them, feel free.

I may have been unconsciously influenced by the dice in +Robin Laws' Feng Shui, as I play tested it recently. This mechanic has a similar shape, but it avoids the open-endedness of that system (which I know really bugged my wife) and also breaks down the results into multiple bands of effect.

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