D&D General Substituting 3Z7 for D20

[UngeheuerLich]

I’d have a success with one 7 mean something extra, two 7’s something great, and three 7’s would be ungodly.

With at least two 7s you are quite close to 5%. So that will work well enough if you like the idwa of a bell curve.

 

[Flamestrike]

Triple 0s = fumble

Count me out.

 

[EzekielRaiden]

I'm not a math person. Can you quantify how drastic the difference is for a DC10 (or DC11) and a DC15 or DC20 under a bell curve like this?

For a uniform distribution like d20, +1 is always equivalent to 1/N, where N is the number of sides on the die. So long as failure remains an option, +1 is always an increase of 0.05 (5%) to the probability of success.

For the distribution you're discussing, it would be as follows, assuming that you are using "meet or beat" rules.

DC 9: 68.38%
DC 10: 59.38%
DC 11: 50% (exactly)
DC 12: 40.63%
DC 13: 31.54%
DC 14: 23.44%
DC 15: 16.41%
....
DC 19: 1.95%
DC 20: 0.78%

So, a +1 is the same as reducing the DC by 1. That means, at the center of the bell curve, +1 is equivalent to about 9.5%, roughly double the benefit of +1 in a uniform distribution. At DC 15, +1 is equivalent to almost exactly 7%, and at DC 20, +1 is equivalent to just over 1%.

At the edges of the bell curve, modifiers become nearly worthless unless they're huge. At the center of the bell curve, modifiers have a massive swing--the difference between DC9 and DC 12 is huge. It's equivalent to going from "you succeed twice as often as you fail," which feels like "normal" difficulty to most players, over to "you fail twice as often as you succeed," which is going to feel like absolute garbage for most players. A -2 or -3 penalty when near the center of the curve is terribly punishing; a +2 or +3 when near the center of the curve means nearly guaranteed success.

Perhaps these are desirable effects for you; but you may wish to consider the impact on player psychology, as noted.

 

[LordEntrails]

In conclusion, 3Z7 would make the game very swingy. And the Adv/Dis mechanic would be less impactful.

And I haven't heard the question asked yet, but it's always something you should ask yourself when considering these things: What are you trying to accomplish? Is there a "problem" you want to fix? A mechanic you don't like?

 

[Lakesidefantasy]

In conclusion, 3Z7 would make the game very swingy. And the Adv/Dis mechanic would be less impactful.

And I haven't heard the question asked yet, but it's always something you should ask yourself when considering these things: What are you trying to accomplish? Is there a "problem" you want to fix? A mechanic you don't like?

Wouldn't 3z7 make it less swingy and more predictable? Maybe I misunderstand what swingy means.

 

[LordEntrails]

Wouldn't 3z7 make it less swingy and more predictable? Maybe I misunderstand what swingy means.

So you have a preplanned encounter, you set the DC at 15 (or you have an NPC with an AC of 15, etc). Now take the average party that has a +5 on their skill check (or attack, etc). Great, they odds of success are basically 50%. But, now you take the average party that has a feat, magic item, or some combination that gives them a +6, they now have a 59% success chance. Or if they have a +7 they suddenly have a 68% chance. Swingy.

Or just look at attacks within the party. The fighter has a +7 attack against the AC15 and hits 68% of the time. But they rogue only has a +5 so he hits 50% of the time and the poor sorcerer with his +3 only hits 30% of the time. Swingy.

If you are not perfectly balanced or optimized, you suddenly are not comparable to other in your party or the encounter goes from too easy to too hard.

 

[DND_Reborn]

Wouldn't 3z7 make it less swingy and more predictable? Maybe I misunderstand what swingy means.

Yes. Ignore anyone who says otherwise.

 

[Lakesidefantasy]

Hmm, what's that on my shoe? Did I just step in something?

 

[Flamestrike]

You get a flatter bell curve with 2d10, and you can easily add Adv/Dis by making it 3d10 (drop the lowest or highest depending on adv or disadv).

For crits they trigger if both dice come up with 9's or 0's (4 percent chance). Champions get this buffed to 8, 9, 0 (roughly 9 percent) and then finally 7, 8, 9, 0 (16 percent)

 

[CleverNickName]

It's probably not going to create a problem, per se. You can still play the game just fine, but the dice rolls will be more predictable and less "swingy." It will effectively remove critical hits and critical failures by making them so incredibly rare, too. But maybe that's what you're going for?