D20 vs 2D10

[DrZombie]

I seriously doubt I'm the first one to think about this, but my major house rule is that I don't use D20 for skill checks and attack rolls, but 2d10.
The reason is simple, a D20 is a linear system, while 2d10 follows a Gauss-curve of probability, meaning that you're far more likely to roll in the 8-14 region. Very high rolls and very low rolls are much more unlikely.

Why do i do this?
- a 1 in 20 chance of fumbling is extremely silly. Imagine surgeons killing one in twenty people (and yes, you can't "take 10" because failure is unfavorable.... )Chances of roling a 2 in 2d10 is very low, and therefor i hear dreadfull gasps of horror when one of my players comes up snakeeyes, they know it's gonna hurt.

- The element of chance is still present, but it is lessened. Skill ranks are therefore more important. Skill checks are more predictable, if you know the DC you'll have a better chance of predicting success.

-Threat ranges are increased by 1, but you use the original rage for things like keen or improved crit, then add 1 (for example a bow would have a TR of 19-20, but with improved crit it would be 18-20).

- Less likely chance of getting a lucky hit, so tough creatures get a lot tougher, watch out for high CR encounters.

 

[FireLance]

- a 1 in 20 chance of fumbling is extremely silly. Imagine surgeons killing one in twenty people (and yes, you can't "take 10" because failure is unfavorable.... )

While your 2d10 system is interesting, I'd just like to point out a couple of rules errors:

1. You don't have a 1 in 20 chance of failure on skill checks, only on attack rolls and saving throws. A character with a wisdom of 16 and 11 ranks in Heal (+14 to skill checks) will always be able to stabilize a dying ally since he will succeed at the DC 15 check even if he rolls a 1.

2. You seem to have mixed up the rule for taking 10 with the rule for taking 20. You cannot take 20 if there is a penalty for failure since it basically means that you are trying to do the task again and again until you get it right. This is why it takes 20 times as long. However, you can take 10 on any check as long as you are not under stress (perhaps this is why surgeons don't operate on family members as a rule). It means you are concentrating on the task and doing it carefully. You won't get exceptional results, but you won't make silly mistakes either. Also, it's a common misconception, but taking 10 requires the same amount of time as a normal attempt; it does not take 10 times as long.

 

[Dalamar]

But because performing a surgery would be an application of the Heal skill and skills don't have automatic successes/failures (only attack rolls and saving throws do), this isn't technically a valid reason to move from 1d20 to 2d10.
Secondly, you can Take 10 even if there is a chance for a Bad Thing(tm) happening. From the 3.5 PHB, p.65 under Taking 10: "When your character is not being threatened or distracted, you may choose to take 10." They even use Climb, on which failing by 5 or more means you fall, as the example skill on taking 10. Only taking 20 is impossible if failure brings unfavorable results.
Edit: Seems FireLance posted the same thing about skill success/taking 10 while I was counting the chances on rolling 12 or over with 2d10.

And the counting of success probability gets a lot harder with 2d10. Lets use an example of scoring a success against DC 16 with a +4 total bonus.
d20: 16-4=12, so that's how high I need to roll, since every every side of a d20 has 5% chance to come up, I have a 45% chance to score a success.
2d10: 16-4=12, so the total of my two dice needs to be that high. Lets see... the dice could come up 10 and 2, 10 and 3, 10 and 4 etc, garnering 9 chances out of 56 (the number of different combinations if you don't take into account the order in which the dice are looked at), or they could come up 9 and 3, 9 and 4, 9 and 5 etc but discounting the chance of 9 and 10 since we already figured that in, garnering 7 chances out of 56 for a total of 16 chances so far. Of course, the dice could land 8 and 4, 8 and 5 etc, but discounting '8 and 9' as well as '8 and 10' since those were already counted, increasing the chance by 5. Finally it comes to 24 possibilities out of 56, or roughly 43%. Yes, a lot easier to count (unless you have some kind of formula that I'm not aware of).

 

[DaveStebbins]

- a 1 in 20 chance of fumbling is extremely silly.

If a natural 20 is only a threat, and must be confirmed with a second attack roll before it is a critical hit, why would EVERY natural one be a fumble?

 

[AeroDm]

That is a really interesting idea, but I don't think I'd use it for D&D. I think that D&D thrives because of the randomness inherent in the system and removing that randomness removes a lot of what makes D&D D&D. I think that this system would work well in non-standard D&D games with vita/wounds and the other popular subsystems because IME randomness destroyes those systems.

 

[Michael Morris]

If a natural 20 is only a threat, and must be confirmed with a second attack roll before it is a critical hit, why would EVERY natural one be a fumble?

Natural 1 is a miss. d20 has no official fumble rules.

 

[Coredump]

Aarrrgggghhhh!!!!!

Sorry, this is kind of a valid idea, but it just doesn't really make sense, and it surfaces every few months...


The point of using the D20 die, is to *simulate probability*. Whether this probability is simulated using a bell curve, poissan curve, linear 'curve', etc. MAKES NO DIFFERENCE. In reality all your proposal does is *change the percentage*

For instance, it is determined (by the game designers) that fighter A has a 25% chance of hitting monster X. This is reflected by the BAB of the fighter, and the AC of the monster. Therefore it takes a roll of 16 on a D20 to hit. What you are doing is decideing that there is really only a 21% chance of hitting (NOTE: most of these percentages are estimates, don't feel like doing a real one for the 2D10 at this point) so you change it to a 16 on 2D10, which is the same as a 21% chance of success. You could have just as easily changed the AC by one, and gotten the same basic result.

What you are doing, however, is greatly changing the effect of magic in certain situations. If Fighter A needs a 10 to hit a creature, getting a +1 will give a big increase; the change from an 18 to a 19 isn't a very big increase (total hits, yes it is a big percentage increase) Currently, a +1 always lets you hit on 5% more swings. your change will mean a +1 will hit sometimes 9% more often, and sometimes 1% more often.

The point is (and sometimes difficult to see) is that a D20 does NOT give linear results, it gives *binary* results, success or failure, the chances of one or the other is determined by the roll. Changing to 2D10 does not change this.

.

 

[ichabod]

The reason is simple, a D20 is a linear system, while 2d10 follows a Gauss-curve of probability, meaning that you're far more likely to roll in the 8-14 region. Very high rolls and very low rolls are much more unlikely.

2d10 is not a Guassian curve. The more dice you roll, the more you approach a Guassian curve, thanks to the central limit theory, but 2d10 would not be enough to justify use of a Gaussian approximation. You need at least three dice before it even looks Gaussian.

-Threat ranges are increased by 1, but you use the original rage for things like keen or improved crit, then add 1 (for example a bow would have a TR of 19-20, but with improved crit it would be 18-20).

- Less likely chance of getting a lucky hit, so tough creatures get a lot tougher, watch out for high CR encounters.

How much less?
Threat range 20: d20 5%, your way 3%, d20 keen 10%, your way keen 6%
Threat range 19-20: d20 10%, your way 6%, d20 keen 20%, your way keen 15%
Threat range 18-20: d20 15%, your way 10%, d20 keen 30%, your way keen 28%

As you can see, this shift the balance towards larger threat ranges. Threat range 20 loses 40% of it's chance to threaten, while 18-20 keen only loses 7%.

 

[DaveStebbins]

Natural 1 is a miss. d20 has no official fumble rules.

I realize that. Let me rephrase. The original poster said that he didn't like rolling a d20 for attack rolls and skill checks. The first reason posted to support this was that a 1 in 20 chance of fumbling is silly.

Since 'fumbling' is normally used in relation to an attack roll which has not only failed but backfired, my question was why he rules that EVERY natural one is a critical failure, when there are already mechanics in place for which not every natural 20 is a critical success.

If the statement was used in relation to skill checks, it has already been noted by others that a natural one does not automatically fail. Additionally, as in the combat example above, a failed skill check with a natural one does not have to represent some sort of critical failure, only lack of success.

I apologize if I was not clear in my original response.

 

[mroberon1972]

Here is a simple d20 rule we use for skills:

If you roll a natural 20, reroll again and add the result to the previous total.

If you roll a natural 1, reroll again and subtract the result from the previous total.

Keep doing this until the player stops rolling 20's or 1's...

No natural failures or successes, but they can sometimes pull off some crazy stunts. They can also fail so horribly as to cause all the bards of the world to weep.



We like it...

Mr. Oberon