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D20 to 2D10


Homebrew


I always thought the D20 systems suffered from their eponymous die of choice: 1 to 20 is quite a large range of result in relation to the flat bonus a character can generate in the beginning and the the fact that each result has the same probability hamper the capacity of players to estimate how their character would fare in face of a given threat.

And so I thought, why not makes the roll with 2D10 instead when the PC are in some way competent with what they must roll? This would bring the stability I was seeking and help players gauge their prospective performance as the can bet on the median result of 11 which as become far more probable.

The divers checks would get easier to beat but as stated the PC wouldn't get this benefit on all of them and I think about giving the same advantage to important foes and nemesis.

With that in mind do you think it could works without upsetting the balance of the game to much? As in being able to use AP without buffing encounters and challenges.


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The altered distribution would affect crit rate. How much this affects your game is dependant on how many builds choose to focus on criticals.


What you'll lose is some of the "swinginess" of the d20 system. The Pros and Cons are the same: You'll get a lot more "average" results, and very few extremes.

What this does mean is that combats will probably go longer, and you're a lot less likely to see a critical hit swing the course of a fight.

The other thing that you'll want to consider is that on a bell-curve system bonuses no longer have a flat +5% for each +1.

I don't think it will change the balance of the game, because both the PCs and the NPCs will have the same effect. But I think you'll find things become more predictable and combats take longer.


I had thought about crits but forgot to mention it.

I would translate the D20 probability of critical threat range to % and differentiate the D10 in the 2D10 to get a D100 reading thus keeping critical distribution the same without the need for additional dice roll.


You completely eliminate the possibility of a critical miss.

With 2d10, there is no way to roll a 1. The lowest roll is 2


This is the closest you could probably get for critical rules:

Critical threat ranges change as follows:
20 becomes 18-20 (6% chance) and is considered a natural 20
19-20 becomes 17-20 (10% chance)
18-20 becomes 16-20 (15% chance)
17-20 becomes 15-20 (21% chance)
15-20 becomes 14-20 (28% chance)

A roll in the range of 2-4 is a critical miss (6% chance)

This stays fairly close to the traditional odds. It does give a slightly better chance of a natural 20 or critical miss, but you could always choose to reduce the range slightly if you feel it's a problem. Due to lack of granularity there is no way to map a 16-20 critical threat range to 2d10, but I don't think there's any way to actually get a 16-20 threat range so that's mostly academic.


CrystalSeas wrote:

You completely eliminate the possibility of a critical miss.

With 2d10, there is no way to roll a 1. The lowest roll is 2

Sorry if I was not being clear, my precedent post also applied to critical misses as well, since the disappearance of the of the 1 result was not lost on me.

Dasrak wrote:

This is the closest you could probably get for critical rules:

Critical threat ranges change as follows:
20 becomes 18-20 (6% chance) and is considered a natural 20
19-20 becomes 17-20 (10% chance)
18-20 becomes 16-20 (15% chance)
17-20 becomes 15-20 (21% chance)
15-20 becomes 14-20 (28% chance)

A roll in the range of 2-4 is a critical miss (6% chance)

This stays fairly close to the traditional odds. It does give a slightly better chance of a natural 20 or critical miss, but you could always choose to reduce the range slightly if you feel it's a problem. Due to lack of granularity there is no way to map a 16-20 critical threat range to 2d10, but I don't think there's any way to actually get a 16-20 threat range so that's mostly academic.

As said the roll would be two differentiated D10, the addition being the check result and the D100 reading informing on the possibility for a critical hit or miss. Therefore the critical hit or miss can be based on the same probability than with a D20 (or even tweaked if need felt).


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so now instead of 1 chance to get a miss you now have 5 chances to have a miss..... really doesn't seem fair to martials


One potential drawback is if you are doing something outside of your specialization you will have a significantly reduced chance to succeed through pure luck.

For example:

Fighter with +10 to hit against AC 18, this benefits him lots since he now has a 79% chance to hit vs a 65% chance.

Now let's say there is a scenario the whole party is down except the wizard, he is completely out of offensive spells, the BBEG with AC 18 is severely wounded and almost dead. The wizard heroically picks up the fighters weapon and attacks the bad guy. Lets give him a +2 (since the wizard most likely would be not proficient and would dumped strength ).

The wizard normally would hit 25% of the time but with a 2d10 system he would only hit 15% of the time.

This would carry into anyone trying to do something they are not "good" at (Heavy Armour fighter rolling acrobatics, dex rogue making a strength check).

How much this would come into play would vary a lot though, depending on your GM style. If you don't make the PC's act out of their comfort zones/builds much it would come up a lot less.

Edit: I realized the wizard is a bad example since they most likely have an offensive cantrip...


Flamephoenix182 wrote:

One potential drawback is if you are doing something outside of your specialization you will have a significantly reduced chance to succeed through pure luck.

For example:

Fighter with +10 to hit against AC 18, this benefits him lots since he now has a 79% chance to hit vs a 65% chance.

Now let's say there is a scenario the whole party is down except the wizard, he is completely out of offensive spells, the BBEG with AC 18 is severely wounded and almost dead. The wizard heroically picks up the fighters weapon and attacks the bad guy. Lets give him a +2 (since the wizard most likely would be not proficient and would dumped strength ).

The wizard normally would hit 25% of the time but with a 2d10 system he would only hit 15% of the time.

This would carry into anyone trying to do something they are not "good" at (Heavy Armour fighter rolling acrobatics, dex rogue making a strength check).

How much this would come into play would vary a lot though, depending on your GM style. If you don't make the PC's act out of their comfort zones/builds much it would come up a lot less.

Which is why I stated my intent to make the 2D10 roll exclusive to things PC are "competent" with in some way (to be defined), thus if you act in your specialty you stabilize your chance but acting out of it is akin to letting it up to luck.

For instance my first take on it was for class skill: if it's a class skill you get to roll 2D10, if not you get 1D20.

For attack roll I was hesitating: getting it with proficiency seems a bit too much but getting it with some class ability or feat (let's say weapon focus) a bit restrictive.


CrystalSeas wrote:

You completely eliminate the possibility of a critical miss.

With 2d10, there is no way to roll a 1. The lowest roll is 2

I think you underestimate my capacity to critically fail at key moments... I'd find a way...


Enomiel wrote:
Flamephoenix182 wrote:

One potential drawback is if you are doing something outside of your specialization you will have a significantly reduced chance to succeed through pure luck.

For example:

Fighter with +10 to hit against AC 18, this benefits him lots since he now has a 79% chance to hit vs a 65% chance.

Now let's say there is a scenario the whole party is down except the wizard, he is completely out of offensive spells, the BBEG with AC 18 is severely wounded and almost dead. The wizard heroically picks up the fighters weapon and attacks the bad guy. Lets give him a +2 (since the wizard most likely would be not proficient and would dumped strength ).

The wizard normally would hit 25% of the time but with a 2d10 system he would only hit 15% of the time.

This would carry into anyone trying to do something they are not "good" at (Heavy Armour fighter rolling acrobatics, dex rogue making a strength check).

How much this would come into play would vary a lot though, depending on your GM style. If you don't make the PC's act out of their comfort zones/builds much it would come up a lot less.

Which is why I stated my intent to make the 2D10 roll exclusive to things PC are "competent" with in some way (to be defined), thus if you act in your specialty you stabilize your chance but acting out of it is akin to letting it up to luck.

For instance my first take on it was for class skill: if it's a class skill you get to roll 2D10, if not you get 1D20.

For attack roll I was hesitating: getting it with proficiency seems a bit too much but getting it with some class ability or feat (let's say weapon focus) a bit restrictive.

Ah well then no issue there. Even then it's a minor issue, I have ran Iron Kingdoms RPG games which uses 2d6 base system and it worked fine. Just changes how the players play a little


Lady-J wrote:
so now instead of 1 chance to get a miss you now have 5 chances to have a miss..... really doesn't seem fair to martials

I am not an expert on probability so I might be missing something but I don't see the difference in treatment (1/20 vs 5/100).


Enomiel wrote:
I don't see the difference in treatment (1/20 vs 5/100).

There isn't any difference.

But if players are not very mathy, they might make the same error and (irrationally) feel like the odds have be fiddled with.


if you make it so they fail on a 2-5 in addition to 1 something that could have hit on a 2 now misses


Lady-J wrote:
if you make it so they fail on a 2-5 in addition to 1 something that could have hit on a 2 now misses

They would fail on five result out of the hundred possible on the D100, making it the same chance to fail than one result out of twenty (the 1 on 1D20).

This should not be the classic 01 to 05 to avoid high addition result being fail though (since 0 = 10 on the D10). So maybe something like 11, 12, 21, 13 and 31 being the fumble with this system.


i still stand by the minimum number value and only the minimum number value should be considered in automatic miss territory and the maximum and only the maximum value should be in automatic teritory


Lady-J wrote:
i still stand by the minimum number value and only the minimum number value should be considered in automatic miss territory and the maximum and only the maximum value should be in automatic teritory

Well you are of course free to think this, but my post was about tweaking the D20 system with some use of 2D10 in certain circumstance, the consequences of such tweak, possible problems and their solutions.

Your principle of critical miss/hit being reserved to the minimal/maximal number value is all well and good, but it's all it is: a principle. It doesn't address the points we were talking about, nor does it bring any new one into light and is therefore irrelevant to the question at hand.


Enomiel wrote:
Lady-J wrote:
i still stand by the minimum number value and only the minimum number value should be considered in automatic miss territory and the maximum and only the maximum value should be in automatic teritory

Well you are of course free to think this, but my post was about tweaking the D20 system with some use of 2D10 in certain circumstance, the consequences of such tweak, possible problems and their solutions.

Your principle of critical miss/hit being reserved to the minimal/maximal number value is all well and good, but it's all it is: a principle. It doesn't address the points we were talking about, nor does it bring any new one into light and is therefore irrelevant to the question at hand.

in a 2d10 system 2 would be the most minimum value so 2 would be a miss, and 20 would be an auto hit just like in 1d20 systems making 2,3,4,5,and 6 count as an auto miss just because you want to switch up the rolling system is going to screw over the martials way more then just the single d20 only failing on a 1, and adjusting the critical threat range on the higher end will make crits way to available which may seem like a boon to the martials at 1st but will mean they will be taking a lot more crits to the face during the campaign meaning they are more likely to die as they are generally the ones taking the hits for the party so the game turns into i either crit this thing for lots of damage or i miss horribly with little to no middle ground or normal hits


Lady-J wrote:
...in a 2d10 system 2 would be the most minimum value so 2 would be a miss, and 20 would be an auto hit just like in 1d20 systems making 2,3,4,5,and 6 count as an auto miss just because you want to switch up the rolling system is going to screw over the martials way more then just the single d20 only failing on a 1, and adjusting the critical threat range on the higher end will make crits way to available which may seem like a boon to the martials at 1st but will mean they will be taking a lot more crits to the face during the campaign meaning they are more likely to die as they are generally the ones taking the hits for the party so the game turns into i either crit this thing for lots of damage or i miss horribly with little to no middle ground or normal hits

I thought you were just being adamant on cirts being reserved for min/max number value, but in fact you seem not to understand the way I suggest to determine critical hit and miss range, which gives the exact same chance to get a critical hit/miss than with a D20 while using 2D10.

Try reading again my suggestion and ask for explanation on the points you didn't understand but as long as you do not get what I meant your contribution will amount to nothing as it will be based on mistaken premises (or you are just trolling and it amounts to nothing either way).


The more I mull this over, with the expanded range for criticals, the more I think you might be better off simply expanding the amount of tasks that characters can take 10 or take 20 with.

A separate d20-based game (Mutants & Masterminds) had an ability (akin to feats) called "Skill Mastery" that allowed you to Take 10 even in stressful situations. Perhaps that could be ported over for all class skills (that the character has at least one rank in)?

I think the math is solid for the expanded range of criticals - but at the same time, I think it'll be far less intuitive for the players and will lead to a lot of confusion (as we can see with Lady-J).


AaronUnicorn wrote:

The more I mull this over, with the expanded range for criticals, the more I think you might be better off simply expanding the amount of tasks that characters can take 10 or take 20 with.

A separate d20-based game (Mutants & Masterminds) had an ability (akin to feats) called "Skill Mastery" that allowed you to Take 10 even in stressful situations. Perhaps that could be ported over for all class skills (that the character has at least one rank in)?

I think the math is solid for the expanded range of criticals - but at the same time, I think it'll be far less intuitive for the players and will lead to a lot of confusion (as we can see with Lady-J).

I own M&M so I'm familiar with this solution, I thought about it but the complete suppression of a roll didn't sit well with me, we tried before but it proved somewhat of a mood killer. I think it's indeed simpler though.

I'm not worried about my usual players, they all have a solid understanding of math and the idea of this modification came from our discussions about boardgames with dices. Newcomers might be put off but I usually don't include home rule with them unless they are a necessary fix to the game as written.


I had same idea about making the characters more regular, by adding more dices that add up to 20. 1d20 => 2d10 => 2d6+1d8 => 2d6+2d4 => 5d4 , and so. They also increase the expectation of the roll. Furthermore it does not generate a gap so quick between levels, which is a far more realistic option.

As some people has stated the main problem is the criticals. If you fix the critical at something like 17 it is much better. But of course this arises other problems.


You could also keep 20 but add 1 to each crit multiplier.


The way I've imagined the automatic success/failure working using the 2d10 system is treating the 20 and 2 as 20 and 1 respectively, but expanding critical range to keep the odds about the same (as Dasrak did). Point is reducing the luck factor without breaking the mechanics after all.

Taking 10 should probably be boosted to taking 11 using this, since the average roll is now 11 rather than 10.5. Taking 20 I feel would be fine to still take the same length of time to do.

You might want to consider increasing basic DCs of everything by 1 for the same reason that you should take 11. That is, base AC is 11, save DCs are 11 + level + modifier. It's kind of an awkward toss up between making things slightly easier by having a higher average and making things harder by effectively reducing the highest value you can get.

Probably the biggest and most obvious change is power gaps, which become much more pronounced. Say you hit on a 4+. That's a 6% chance of missing. A +1 bonus drops that by 3%, while a -1 penalty raises it by 4%. If you need an 11, +1 bonuses and -1 penalties change it by 9% or 10% respectively.
Basically, if you're behind, it takes a lot to catch up, and if you're about even, it takes very little to shift the balance in your favour. You'll probably find boss fights become much harder and see more tactical play. Taking that move action to jump on the table for the +1 high ground bonus is more worthwhile when it boosts your 10 to an 11, changing hit odds from 45% to 55%, compared to the standard 45% to 50%. Dropping prone to avoid arrows could reduce that 45% chance of hitting you to 15%, an effective +6 to AC using the d20.

Aid another becomes fairly valuable, since even a lightly trained character will be able to succeed easily and a +2 bonus can be up to a +19% chance of success.

Think that's about all the things I've considered when I looked at it myself. Haven't actually tried it though, so how valid any of this is in practice is debatable.


Pathfinder Companion, Roleplaying Game Subscriber

This seems like it will result in a less enjoyable game.
Skills: There is already the option to take ten if you need an average result, so this just hurts the option of gambling on getting a good outlier.

Attacks: Pathfinder combat eventually only misses on low numbers for initial attacks. This greatly reduces the odds of missing by making results average. Haste and archery builds get even better, and combat begins to get predictable.

Saves: Opposite problem here. Often, saves need to be something better than average. Multi-save save-or-die spells that give a couple chances to not die become stronger, because those good rolls become rarer. Boosting DCs becomes huge, because each point of DC is even more powerful than the old system.

Overall: There is more rolling, more addition, and fewer compelling/memorable/exciting rolls. Nobody misses, and casters are pushed to cheese their DCs as high as possible.

Recommendation: Use 2d10 as a replacement for taking 10. It’s a little more interesting, and does a good job of representing doing something carefully. Combat and saving throw math are more finicky.


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Thanks for all the comments. Wolin's bit on the maths behind it was particularly insightful as I didn't crunch the numbers myself yet.

I'll see to implement it for my next table if the players are interested to experiment a bit and report how it goes thereafter.


Hadn't thought about it, but reroll spells and effects are fairly terrible with this since you don't get the large swings. Or less rewarding or satisfying, anyway. You can get interesting mechanics you couldn't with a d20 though. Reroll a die of your choice would have to be the quirk (Although you may want to do/allow both, depending on the quality of the roll).

Say there's an average roll of 11 with a 10 and a 1. Rerolling both isn't particularly fabulous: there's a 10% chance of nothing happening, 60% chance of being up to 4 higher or lower, leaving 15% each for a good 16+ roll or an awful 6- roll.
If you can force someone to reroll just the 10, or reroll your own 1, this becomes rather better. Now it's a 10% chance of nothing, a 40% chance of being 4 higher (or lower) and a 50% chance of one of the rare 16+ (or 6-) rolls. And, importantly, a 10x higher chance of getting an automatic success from the 20 or failure from the 2.
For comparison, on the d20, the same roll is 5% of nothing, 20% a little better, 25% each for a little worse, 5- and 16+. You're less likely to do well, but more likely to get something fabulous compared to rerolling both, and rerolling 1 is strictly better.

With this in mind, you might like to make reroll effects more common as a means of getting to high or low numbers more easily/at all. I've toyed with the idea of giving immediate action rerolls based on charisma to make it a more useful stat (and since it's the most thematically close to luck).

Other thing you could do is unusual stuff with doubles. If you're familiar with Shadowrun's glitch system you could use a variant of that. Basically, it's a "You succeed, but..." or a "You fail, but..." kind of system. At its simplest, you could keep odds of critical success/failure the same as d20 and make, say, double 1-5 auto fails and double 6-10 auto success.
There's a degree of narrative addition that it can make it more interesting, if you're creative, or gives you an easier way of rewarding players who try something cool or inventive but fail because of a bad roll. Or punish players who do things like insult people to their face but still succeed on the diplomacy check because they have +56415338 to their check.


Adventure Path Charter Subscriber
Lady-J wrote:
so now instead of 1 chance to get a miss you now have 5 chances to have a miss..... really doesn't seem fair to martials

It’s not about the number of rolled results that would be auto-misses. The important metric is the probability of those results being rolled when it comes to being fair.

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