Consquences of using 2d10 instead

[ronpyatt]

tesral's System thread got me to thinking about this. This may be a bit premature with 4th Edition being so new, but what might happen if one were to change the basic die roll from 1d20 to a 2d10? (which changes the roll range from 1-20 to 2-20)

What 4e rules would be affected?
Would it trash any particular class or race more than others?

You might be asking "why would anyone want to do that?"!

[agoraderek]

off the top of my head, without doing the math (or googling a chart from someone who has), i'd say that crits may be a bit more rare, and obviously you can't roll a one, but other than that, all using 2d10 over 1d20 would change is the number of "middle" rolls you get, as you are changing from a flat 5% probability for each number to a slight bell curve.

[Oedipussy Rex]

off the top of my head, without doing the math (or googling a chart from someone who has), i'd say that crits may be a bit more rare, and obviously you can't roll a one, but other than that, all using 2d10 over 1d20 would change is the number of "middle" rolls you get, as you are changing from a flat 5% probability for each number to a slight bell curve.

No, not a "slight" bell curve, a definite bell curve. And crits and fumbles, if used (fumble being a 2) would occur 1% of the time each.

Rolling 2d10 for To-hits also plays havoc with the system. With a d20, the chance to hit is a smooth progression: each additional point of AC means a 5% smaller chance to hit. With 2d10, each point of AC over 11 (assuming an ascending AC) creates an ever greater chance to miss. That is, the difference in the chance to hit an AC of 14 and an AC of 13 is greater than the difference between AC 13 and AC 12.

[agoraderek]

No, not a "slight" bell curve, a definite bell curve. And crits and fumbles, if used (fumble being a 2) would occur 1% of the time each.

thanks for the deeper explanation. so, since 4e doesn't have to worry as much as earlier editions with the game "breaking" a bit at high levels (as far as i can tell, "plusses" to bab aren't as big a deal in 4e, mostly its the powers that influence higher level play), what would switching to that do for the balance 4e is trying to achieve? would a bell curve disrupt the system since it was written with the linear d20 probabilities in mind?

[Oedipussy Rex]

I was editing my post to add a little more information while you posted this.

As for "balance," I couldn't say. Don't have 4e, don't plan to get 4e. Hell, I don't have 3e or 2e, for that matter.

[agoraderek]

I was editing my post to add a little more information while you posted this.

As for "balance," I couldn't say. Don't have 4e, don't plan to get 4e. Hell, I don't have 3e or 2e, for that matter.

i'm buying into the paizo stuff myself, their campaign setting is pretty cool, just asking for ron's sake, actually.

i do see how applying a bell curve can screw up the implied probabilities, now that you point it out, though. i hope that helps him decide what to do in his group.

[tesral]

Oh Ghodd. You would bork the whole system. Toss the balance out the window. Indeed you will have invented an entirely new system which has yet to be play tested.

As a linear system d20 is a game of percentages. It is never stated in so many words, but that is the game.

Joe Average, BAB 0, AC 10. One Joe has a 50% chance of connecting on another Joe. While you have a 5% chance to roll any given number the target number system "Number or better" renders a percentage chance of success. The game mechanic revolves around bettering your percentage to hit and worsting your percentage to be hit. (Enter scaling problems, another thread)

Changing to the 2d10 tosses a bell curve in place of the linear progression. (no I don't have a 2d10 bell curve handy either.) But without altering anything else you have improved Joe's chance to hit Joe because 11 becomes the middle of the curve and the most common number rolled. The chance of success with BAB 0 against AC 10 just improved.

The value of a +1 is also changes because it gives you a significantly better chance of getting the ends of the curve. (Again sorry no exact math.)

You could do it, but I'd run a lot of math under the bridge before committing to such a move. It's not the same game anymore.

[Valdar]

Half of the Epic Tier feats give you a crit on a 19-20 rather than a 20- with the current system, that means going from 5 to 10 percent of the time. With 2d10, that goes from 1 to 3 percent... so you'd probably need to come up with more Epic Tier feats to replace all the ones that the new system makes next to useless...

But that gives me an idea:

Magic Item: Fate Crystal: When shattered (minor action), this crystal subtly affects probability, causing your next roll to be made with 2d10 rather than 1d20.

Then sit back and let the player figure out the implications of using this item...

[ronpyatt]

thanks for the deeper explanation. so, since 4e doesn't have to worry as much as earlier editions with the game "breaking" a bit at high levels (as far as i can tell, "plusses" to bab aren't as big a deal in 4e, mostly its the powers that influence higher level play), what would switching to that do for the balance 4e is trying to achieve? would a bell curve disrupt the system since it was written with the linear d20 probabilities in mind?

Very good point. With 1d20, encounters with monsters 4 levels higher than the characters would normally be within range of a party, tough but doable. But 2d10 reduces the chance of success to the edge of probability.

The encounter threshold would be lower, or rather the encounter depth-of-field would be reduced. As monsters just one level lower than the party level could be beaten far more easily. The focal point of monster encounter levels would shorten to somewhere around 0 to 2 levels above the party level.

I'm actually liking the potential. It means that bonuses (bab, environmental variables, magic bonuses, feats) have a greater significance in a character's performance, and a reduced reliance on probability.

[MortonStromgal]

What happens is that rather than 20 kolbolds being a threat to uber PCs its now 100 kolbolds (nat 20s) and PCs will roll 10s alot more often.

[Webhead]

I've seen suggestions and modifications for using 2d10 and even 3d6 in place of the 1d20. Part of the suggestion for using 2d10 is that you increase "auto failure" to a natural roll of "2" or "3" and "auto success" to a natural roll of "19" or "20". This at least gives you a 3% chance of criticals on either end of the spectrum. Obviously, this changes up critical threat ranges for weapons, so you have to decide how you want to handle that.

They also suggest that high DCs need to be shifted down slightly as your dice probabilities will be more heavily weighted toward results of "10" and "11".

Using 2d10 will produce a more consistent "average" which, in turn, means it will be easier to predict how your PCs will fair against challenges of a certain DC. In the end it just means that extremely high and low rolls will be much more rare which means difficulties need to be shifted closer to the "median" values to keep them relevant and still achievable.

[Tenebras]

....

[Tenebras]

Here's the distribution for 1d20

********************
********************
********************
********************
********************
12345678911111111112
         01234567890

And for 2d10

          *
         ***
        *****
       *******
      *********
     ***********
    *************
   ***************
  *****************
 *******************
12345678911111111112
         01234567890

Each star represents 1%. What you see is that the 1d20 distribution is completely flat, while the 2d10 is a first approximation to a bell curve. 10% of 2d10 rolls are 11. 28% are in the 10-12 range. 44% are between 9 and 13.

Most of the time the game is balanced so you succeed on a roll of 10 or higher. Rolling d20 you get a 10 or higher 55% of the time. Rolling 2d10 you get a 10 or higher 59% of the time.

[ignimbrite]

Half of the Epic Tier feats give you a crit on a 19-20 rather than a 20- with the current system, that means going from 5 to 10 percent of the time. With 2d10, that goes from 1 to 3 percent... so you'd probably need to come up with more Epic Tier feats to replace all the ones that the new system makes next to useless...

But that gives me an idea:

Magic Item: Fate Crystal: When shattered (minor action), this crystal subtly affects probability, causing your next roll to be made with 2d10 rather than 1d20.

Then sit back and let the player figure out the implications of using this item...

love it! Just see their faces deciding if it would be better or if it would give them some sort of an edge.

[Stormhound]

Most of the time the game is balanced so you succeed on a roll of 10 or higher. Rolling d20 you get a 10 or higher 55% of the time. Rolling 2d10 you get a 10 or higher 59% of the time.

Actually, you get 10+ on 2d10 64% of the time, which is a significant shift (roughly the same as rolling 8+ on d20). Hardly surprising, since the average of d20 is 10.5, and the average of 2d10 is 11.

love it! Just see their faces deciding if it would be better or if it would give them some sort of an edge.

If you need a high roll (success number is 13 or higher), go with d20. If you merely need to avoid a low roll (success number is 11 or lower), go with 2d10. And if you need a 12, it's a wash, so save your item.