A new RPG system

Further Scrutinizing the Dice Mechanic

Previously we looked at linear Dice Mechanics and I expressed fondness for a 2d6-2d6 system.  Here we’re going to explore this in a little more depth, see what problems it has, what our options are, and work out any kinks.

Some of the questions that come up are, are “How does the range affect play?”, “What happens with Highest Rolls?”, “Who Rolls?”, “How complex is this?”, etc…

The Base Roll

The 2d6-2d6 system means that for any test, 4 6 sided dice are rolled.  One immediate and obvious complexity is that subtraction is difficult.  For example if I roll [4,5] on the positive die and [2,6] on the negative die the mental process probably goes something like:

  • Okay, 4+5 is 11
  • Um, 2+6 is 8
  • And 11 – 8 is…
  • 3

Conversely if I simply roll [4,5,2,6] and add them together the reasoning is something like

  • 4 and 6 is 10
  • Plus 5 is 15
  • Plus 2 is 17

It’s considerably easier to do the second of those.  However there is a way to make it even simpler.  Every roll is an “opposed” roll.

If you think about it most of you have used Dice minus Dice mechanics before, but when you have it’s been in the form of “opposed” rolls.  You roll your Dice, your opponent rolls their dice, each of you add your score, and then compare.  If each of you were rolling 2d6 for example, you would have the exact same effect as 2d6-2d6.

In fact, many systems haven’t thought through the effect of an opposed roll.  Often you have a certain variance when acting alone, and then a totally different variance when making an opposed check.  That’s no good.  One solution to this could be to have each side roll half the dice on an opposed check, and another solution is to make every check opposed.

Using this system, a check to for example pick a lock might be a Difficult 10+2d6 vs an Ability of 10+2d6, which is exactly identical to Difficulty 10 vs 10+(2d6-2d6).  Who exactly rolls doesn’t particularly matter.  Both sides can roll, or either side can roll and it will have the exact same mechanical effect.  The only thing that might bother some is the idea that a “lock” is rolling for it’s “Defense”, but that’s easy to overcome if you realize that Everything is a Character.

Exploding Dice

d12-d12 has a nice tidy Range of -10 to +10.  However, what happens when you get a 10, or even when one side rolls a 12?  Nothing would be a fine answer for some, but it’s anticlimactic to say the least.  Furthermore, if you’re like me, you don’t like something to be impossible, even if the margin of probability is vanishingly small.  To handle this, I propose exploding dice.  Now there are three different ways I could have dice explode.  I could use 2d6-2d6 and explode on a +10 or a -10, and the dice on that side reroll and add.  For example if it was [6,6]-[1,1], the side that rolled boxcars would roll again and add, and if boxcars were rolled agin, they would add again, etc…  The advantage of this is that while it allows the possibility of extremely high numbers, it has essentially zero impact on the distribution and Standard Deviation because getting a +10 or -10 will only happen once in every six hundred or so rolls.  It is a zero impact way to handle exploding dice.

However, I actually think the distribution on 2d6-2d6 is a little too “tight”.  An alternative is to have every [6] explode.  So a [5,6]-[3,6] would have each side reroll and add the six, and continue rerolling sixes.  For example that might become [5,6,3]-[3,6,6] and since another six was rolled on one side it finally becomes [5,6,3]-[3,6,6,4], totaling 14-19=-5.  This system does have some mechanical flair to it, seeing the boxcar coming up can be thrilling, it has a pretty radical effect on the distribution.  The variance here is magnified substantially, to the point of making it more random than a flat d20.  That variance is way too big.

The final two options are two have each side roll, and if Boxcars comes up for that side, reroll and add continuing to explode boxcars, or roll and add an additional exploding 6.  The first would work out something like this [6,6]-[3,1] -(roll two more 6’s)> [6,6,6,4]-[3,1] -(sum)> 22-4=18.  The second system would be [6,6]-[3,1] -(roll and add a d6)> [6,6,6]-[3,1] -(roll and add another 6)> [6,6,6,4]-[3,1] -(sum)> 22-4=18.

Of these two options the Exploding Boxcars give a higher Standard of Deviation than the Exploding 6.  Personally I find the Exploding 6 to give a range more in line with my thinking, however it is a little harder to explain.

The Living Myth Dice Mechanic

This brings us to our tentative Living Myth Dice Mechanic –

When a character is attempting to act, they take their Ability + Modifiers + 2d6 and compare it to the Difficulty + Modifiers + 2d6.  If two sixes are rolled by either side, that side rolls another d6 and add to the total, if that added 6 is also a six add another d6 to the total until a 6 is not rolled.

Can you see any flaws?  Any thoughts on this mechanic?


3 responses

  1. FYI, you can do “die minus die” without ever doing subtraction.

    For example, instead of rolling d12-d12, just roll two different colored d12s and pick one ahead of time to be the negative die (e.g. black = positive; red = negative). Then instead of subtracting, just use the lowest die (and treat doubles as zero).

    Black 2 and Red 11 = 2
    Black 8 and Red 7 = -7
    Black 3 and Red 3 = 0

    This has exactly the same distribution as d12-d12, but is much faster to read.

    February 12, 2016 at 7:26 am

    • Good point! http://anydice.com/program/7a00

      February 12, 2016 at 3:55 pm

    • This actually brings up a really interesting mechanic, that would be really well suited to a game emphasizing strategy. You can imagine each side has mixed dice pools, or perhaps your attribute determined how many dice (more is better) and your skill determines the number of sides (less is better, but you can always roll higher sides). Then each side secretly picks one dice from what they roll, and whichever side picked the lower dice gets to keep the result.
      This is interesting because you want to pick the highest result that is lower than what your opponent picks.

      February 12, 2016 at 4:14 pm

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