Homebrew 2d10 vs 1d20

[Xeviat]

I've recently been reading up on older D&D and OSR, and systems there often use a 2d6 to determine things. The differences in weights compared to a flat roll, like a 1d12, for those rules makes bonuses and penalties feel different. So, while I'm not actually considering switching to 2d10 instead of 1d20, I wanted to discuss it and just ask what would happen if we did switch?

First, on a roll of 1d20, there is a 5% chance of rolling any given number. On a roll of 2d10, though, you get the following chances:

2: 1
3: 2
4: 3
5: 4
6: 5
7: 6
8: 7
9: 8
10: 9
11: 10
12: 9
13: 8
14: 7
15: 6
16: 5
17: 4
18: 3
19: 2
20: 1

1d20 has an average of 10.5, while 2d10 has an average of 11. But, 11 is also the mode of 2d10, so most rolls will be 11 or higher. This means if we assumed a baseline of +0 against a DC 10 (or +5 vs DC 15, as we'd get from a 16 ability score and a +2 proficiency baseline for "high" score at 1st level, chance to succeed changes from 55% to roll 10 on 1d20 to 64% chance to roll a 10 on 2d10. Curiously, that's around the 65% baseline many of us use when talking about attack vs AC.

How would critical hits work? If we naively kept it as a natural 20, critical hit chance would drop from 5% on 1d20 to 1% on 2d10. But, I had a thought that critical hits could be if you hit AND one of the dice is a 10. Against DC 11 or below, +0 would crit 19% of the time. Every +1 DC would reduce the chance to crit by 2%, until reaching 1% chance to crit against DC 20. At DC 18, you have a 6% chance to hit and a 5% chance to crit. This works out interestingly, showing that most hits that actually get through heavy armor would necessitate being crits, an effect that exists less pronouncedly with the 1d20.

One of the biggest changes switching to 2d10 would be how it drastically increases the strength of higher challenge foes, or strenghtens players when they outmatch weak opponents.

With 1d20 and +0, DC 10 is 55% success, DC 15 is 30%, and DC 20 is 5%.
A +1 bonus increases your chance by 5%, a +2 by 10%, and a +5 by 25% (to a maximum of 95%, since 1 always misses).
With 2d10 and +0, DC 10 is 64% success, DC 15 is 21%, and DC 20 is 1%.
Against DC 10, a +1 bonus is an 8% bonus, +2 is a 15% bonus, and +5 is a 30% bonus.
Against DC 15, a +1 bonus is a 7% bonus, +2 is a 15% bonus, and +5 is a 43% bonus.
Against DC 20, a +1 bonus is a 2% bonus, +2 is a 5% bonus, and +5 is a 20% bonus.

Hard stuff would be made harder, easy stuff would be made easier, and moderate stuff has a nice happy 64% chance. I'm left wondering if this kind of change would make the game feel different. I have played L5R's Roll/Keep system, and that was interesting. I'm just kind of wondering if such a change could facilitate some interesting gameplay.

 

[Zardnaar]

It makes bonuses a lot more important. +3 via ability scores. For example.

 

[sevenbastard]

Back in the 90s we ran a homebrew 2d10 system.

Bell curves are where its at.

 

[Merlecory]

How would critical hits work? If we naively kept it as a natural 20, critical hit chance would drop from 5% on 1d20 to 1% on 2d10. But, I had a thought that critical hits could be if you hit AND one of the dice is a 10. Against DC 11 or below, +0 would crit 19% of the time. Every +1 DC would reduce the chance to crit by 2%, until reaching 1% chance to crit against DC 20. At DC 18, you have a 6% chance to hit and a 5% chance to crit. This works out interestingly, showing that most hits that actually get through heavy armor would necessitate being crits, an effect that exists less pronouncedly with the 1d20.

A 2 parter: First, A roll of 18 or higher would be about a 5% chance, same as on a d20, if that is something interesting to you. For the second, why would changing DC effect crit chance? It doesn't normally (a +1 longsword wouldn't crit on 19-20 in 5e)

Hard stuff would be made harder, easy stuff would be made easier, and moderate stuff has a nice happy 64% chance. I'm left wondering if this kind of change would make the game feel different. I have played L5R's Roll/Keep system, and that was interesting. I'm just kind of wondering if such a change could facilitate some interesting gameplay.

I have had half a mind to do that implement something much like this for skills. This would make "experts" feel like experts, easily doing things that less skilled people struggle to do.

 

[SableWyvern]

If you're talking about just taking a given edition of D&D and changing 1d20 rolls to 2d10 rolls, you've identified the main thing that changes: things that are hard become harder, while things that are easy become easier. The easier/harder to begin with, the more extreme the change is.

A foe that is hard to hit, becomes even harder to hit, meaning it will survive longer and mete out more damage. A foe that is already easy to hit, becomes easier and even less of a threat. A save that's hard to make becomes harder, one that's easy to make becomes easier. Etc..

At the end of the day, the impact all this has is going to depend on what other changes you make around it. Particularly difficult fights might be come nigh-impossible, while relatively easy ones will be complete cake-walks. Of course, if you rebalance your encounters around this new dynamic, then everything changes again.

IMO, If you do change to 2d10 and then also start changing a bunch of other things (modifiers, encounter design, save DCs) to account for this, you're probably better off just going all the way back to square one and designing a coherent system from the ground up, rather than trying to modify every aspect of an existing system.

 

[Jahydin]

I ran 5e for about 5 years straight using 2d10 for Ability Checks (combat was still d20 to maintain the randomness) and I thought it worked great. D20 rolls were just too random for tasks these characters were suppose to be experts.

Worth noting that this goes against the design philosophy of "everyone should be able to give anything a try". To alleviate that, I let every skill listed available for the class to be rolled with their proficiency bonus. Skills they actually chose were rolled with proficiency bonus * 2. This let everyone roll for tasks that were within reason while also allowing those that were actually skilled to shine. Worked much better RAW for me.

 

[Li Shenron]

As already said, the more dice are used, the more the results tend to cluster around average, very quickly with the first added dice and then the effect is less pronounced with any additional die. So the highest and lowest scores become less probable, and outcomes are more predictable: more chances for the stronger to beat the weaker, and any fixed bonus/penalty becomes more important.

Personally I don't think it matters that much in combat. On the long term the PC are going to have a lot of combat encounters in their campaign, and combat swingyness somewhat evens out anyway, but it does encourage the DM not to use monsters significantly stronger than the PC when it requires a lot of luck to beat them.

I would be more interested in using 2d10 for ability checks, because in that case I would prefer skilled PCs to be more reliable, even at the cost of unskilled PCs to be cut off from beating challenges by luck.

For critical hits in combat using 2d10 rolls, there are other options to consider. The core rule establishes that criticals are entirely a matter of luck: 5% in any case (unless you have a special ability or item). But it doesn't have to be: in 3e a critical requires a confirmation roll which does depend on stats. So another option with 2d10 could be not to look at the "natural" dice result but e.g. say that if you score 5+ more than the AC then it's a critical.

 

[Horwath]

I ran 5e for about 5 years straight using 2d10 for Ability Checks (combat was still d20 to maintain the randomness) and I thought it worked great. D20 rolls were just too random for tasks these characters were suppose to be experts.

Worth noting that this goes against the design philosophy of "everyone should be able to give anything a try". To alleviate that, I let every skill listed available for the class to be rolled with their proficiency bonus. Skills they actually chose were rolled with proficiency bonus * 2. This let everyone roll for tasks that were within reason while also allowing those that were actually skilled to shine. Worked much better RAW for me.

for skills, we prefer 3d6.
it's few rolls that can have dire consequences, attacks and saves are rolled 50+ time per combat, so it evens out a little.

but, I do prefer "d12+4" instead of d20.
you still roll only 1 dice, so advantage/disadvantage works, average stays the same(10,5) and we do get little more crits. Everyone loves more crits.

and 5+16 is a much less random than 1-20

 

[Seramus]

For better or worse, the "expected" outcome becomes even more likely, reducing the chance for "unexpected" outcomes and the stories they generate.

Sometimes those stories are silly/swingy and don't make much sense. Sometimes they are legendary.

 

[aco175]

How big of a difference from advantage/disadvantage on a d20 compared to having 2d10, but only using one of the d10s for the A/D? Say there was an attack and rolling d10s I used 1 blue as normal and 2 red taking the best for advantage of those two.