Homebrew 2d10 vs 1d20

[Emerikol]

Minor necro!

IMNSHO, that's reason #1 why I stick with 1d20. It keeps the math fast, and discourages the meta-gaming focus on knowing DCs that 2d10 (3d6, et al.) encourages. It's not about predictability of the dice, it's about predictability of the game.

I beat you to the necro I suppose if it really was a necro.

I think if you are playing D&D changing up the dice is probably more trouble than it is worth.

I think if designing my own game the linear dice for skill checks would drive me nuts. It is very unrealistic. Typically you advance quickly early on when learning but then you plateau and it becomes a lot more difficult. This is one of my challenges with GURPS linear advancement. It's got tons of strengths skill wise so I'm still playing it but that is one area I think about.

 

[Lord_of_the_Mourning]

Will absolutely use this for ability checks. My players always have to have everyone do a separate check for monsters, to see if some one is lying, to intimidate the store keeper into giving them a 1 Gp discount, ect. This should help a little. It's not bad that they are cautious, but it can be a time drag.

 

[Thomas Shey]

That's true and not-true at the same time (and this applies to percentile systems too). While going up one point does, indeed, always mean 5%, it doesn't necessarily mean what people will think in terms of failure/success chance unless they think about it (this is probably what the above poster means by "hit the end of the scale", but even that 5% doesn't mean the same given what the chance of success otherwise is. If you normally need a 10 to succeed at something, then an additional +1 doesn't actully change things in a way that will be meaningful to most people; unless you have a very fine sense of such things, the difference between 50% chance of success and 55% is probably psychologically invisible.

On the other hand, once you get out of that middle 50% (basically, a target number of 6 to 15) it starts meaning more and more to a lot of people; a one in four and a one in five failure chance can feel fairly different (the difference beween needing a 6 and needing a 5).

If anything, this can be less pronounced with 2D10 or 3D6 systems because of the way the probabilities trail off at the top and bottom.

 

[NotAYakk]

Minor necro!

I think the last couple rounds of discussion highlight a factor that may not be immediately obvious: Changing from 1d20 to 2d10 introduces an additional layer of math - and character knowledge - that is needed for system mastery.

One of the biggest arguments for 1d20 is simply it's mathematical elegance: every +1 represents a simple 5% probability change. +1 from this item, +2 from this class bonus, +3 from this whatever. It's trivial for players to understand the math because each +1 means exactly the same thing (until you hit the end of the scale).

In a 2d10 system, the mathematical bonus of a +1 varies. A lot. If the DC is 20, granting a +1 changes the odds from 1% to 3% success. So that +1 is a 2% change. But if the DC is 11, a +1 changes the odds of success from 55% to 64%. A 9% difference. That +1 is worth a lot more on DC11.

And knowing this math isn't just rewarding players who are better at better at statistics, its rewarding players who memorize the Monster Manual. In order to know if a +1 bonus is a 2% aid or a 9% aid, the players need to know the DC.

IMNSHO, that's reason #1 why I stick with 1d20. It keeps the math fast, and discourages the meta-gaming focus on knowing DCs that 2d10 (3d6, et al.) encourages. It's not about predictability of the dice, it's about predictability of the game.

No, this is an illusion.

If you treat each +1 as 7%, and values over 17 and under 4 as next to impossible (only possible on a "crit" equivalent, like nat 1/20 in d20), your error in your chance of success vs the actual math is small.

In an roll over (or under) system, you don't care about the probability to roll an X, you care about the probability to roll an X or higher (or lower). This is the cumulative distribution.

A small error in a given +1 doesn't matter so long as your estimate of the cumulative probability is good enough.

And a DC 10.5+X vs d20 maps to a DC 10.5 + X*0.7 in 2d10 with a high degree of fidelity. The error outside of the extreme values is small enough that if such a transformation was done to a game and you watched only the the success/failure information of the game (not the numbers rolled), it would be insanely difficult to tell. (I may have gotten a constant wrong, I often mix up *1.4 and /1.4 aka *.7; the real math is sqrt( 2(10+1)(10-1) / (20+1)/(20-1) ), aka something really close to sqrt(1/2), and if you went further you'd probably want to account for higher order moments.)

The complexity you imagine is somewhere between fake and irrelevant to the result of die rolls.

There is no need to memorize the monster manual.

The extreme cases are all in the outlying 5%ish (nat 1/20 territory)

 

[Coroc]

What is the purpose? Are you striving for a more streamlined combat? If you use this system, you maybe should not allow crits at all - and compensate for stuff in the RAW that feature crits somehow. I dunno, in BG3 you can put loaded dice, it basically does the same but puts you on real disadvantage at higher levels, because mobs tend to hit you more often then, because AC can only get so high. Tried it, and deactivated it again. Not to my taste.