D&D General Substituting 3Z7 for D20

I've been toying with the idea of substituting a 3Z7 (which is my entirely made-up notation for what is effectively 3D8-3, but suggesting the dice physically be numbered 0 - 7) for the D20.

Triple 7s = crit, Triple 0s = fumble (I kinda like the implied nomenclature: "7s UP" and "Zeroed Out")

Would this create extreme problems?
 

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TwoSix

Unserious gamer
The mean is the same, the range is only slightly expanded (0-21 instead of 1-20). It has all the classic problems of trying to use a bell curve distribution instead of the d20 systems linear distribution. +1 bonuses are more valuable if the DC for checks is at the peak of the bell curve, and much less valuable for DCs that are higher or lower than the bell curve peak. Additionally, if crit/fumbles are triple 7/triple 0, you're changing crits from being a 1/20 chance to a 1/512 chance; basically going from a once a session or so occurrence per player to closer to once or twice a campaign.
 

With this system we would rarely get a critical hit or a critical fumble. It would be much rarer than getting a1 or 20 on a d20.

Some might consider that a good thing.
 




I’d have a success with one 7 mean something extra, two 7’s something great, and three 7’s would be ungodly.
Could add to that with one 0 means something unusual happens, two 0's something bad happens, and 000 results in something terrible.

if the DC is low then succeeeding even when rolling one 0 or even 00 isn't out of the question, so this would mix things up both for success and failure.
 


The mean is the same, the range is only slightly expanded (0-21 instead of 1-20). It has all the classic problems of trying to use a bell curve distribution instead of the d20 systems linear distribution. +1 bonuses are more valuable if the DC for checks is at the peak of the bell curve, and much less valuable for DCs that are higher or lower than the bell curve peak. Additionally, if crit/fumbles are triple 7/triple 0, you're changing crits from being a 1/20 chance to a 1/512 chance; basically going from a once a session or so occurrence per player to closer to once or twice a campaign.
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?
 

I feel like the corner of the fanbase who got physically angry are 'sometimes we add 2+2' are going to stand for 'we always do 3d8-3'.
If you mean that people will hate on the "Z" notation because it decouples the number of sides on the dice while replacing it with the notion of the "max #" on the dice,... yes, I have already been incinerated with flames on that. Not on these forums, however.
 



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.
 

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?
 

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.
 

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.
 



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)
 
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CleverNickName

Limit Break Dancing
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?
 

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