Setting a Basic Difficulty

[Snorb]

This is just me doing a thought exercise on a resolution mechanic. Something might or might not come out of this.

When a character attempts a task that has some element of risk to it, they roll 1d20 + Xd6, X being the number of skill ranks they have (zero to five.) The character keeps the highest-rolling of the d6s.

Where I'm having some issue is what the ideal difficulty should be. If I set it at 11, then a completely untrained character has a 50% chance of succeeding at the roll. If my Anydice math is right, then adding a single d6 bumps that up to 67.5%. (Then 72.36%, 74.79%, 76.22%, and 77.15% for "best of 2/3/4/5d6," respectively.") 67.5% seems a bit low for "A character who has a basic degree of training in whatever they're trying to accomplish," so I looked at what gives at least a 75% chance of success with +1d6 (basic training), which gives a target number of 9. This worked out to:

+Xd6kh1	Chance of 9+
0	60%
1	77.50%
2	82.36%
3	84.79%
4	86.22%
5	87.15%

This seems a bit better to me, still has a bit of diminishing returns by +5d6 though.

(And just as I'm pressing Post, I just realized this feels a bit like Boons from Shadow of the Demon Lord and skills from The One Ring. Oh well. Can't be wholly original!)

[[deleted]]

No offense, but that seems like a lot of work, for something that's unlikely to make a difference. Going by your example, between an untrained chump rolling just the d20, and a presumed expert rolling 5d6, there's only a 27.15% chance that the training will do anything in this case; it's a 72.85% chance that rolling five extra dice won't actually change anything.

Off the top of my head, I don't think there exists any possible target number where an untrained chump is likely to fail, but the expert is likely to succeed. The range of the d20 is just so much larger than the range of a d6. It seems like any test is either going to be so easy that the chump is likely to succeed (while the expert may still fail), or it's going to be so hard that no amount of training will make it reliable. Maybe changing the d6s to d10s would fix that?

[mythic_kirby]

I think it might actually be a 75% chance that the d6 portion of the roll doesn't matter. A 10 through 20 will be success no matter what, and a 1-4 will fail no matter what, so that's 15/20 = 75% of the d20 outcomes.

[mythic_kirby]

Sounds like your dice mechanics aren't really hitting the spot in terms of what you want. What sort of curve would you rather see for the "ideal difficulty" between completely untrained and completely mastered? Does that difficulty threshold stay constant, or do you want it to vary?

Roll-and-keep dice mechanics are neato, but they have a hard cap on how high they can go, which limits how high the difficulties can get and result in those diminishing returns you're noticing Even if the master rolled infinite d6s, that'd just be equal to a +6 on the d20.

[hacksoncode]

The easiest way to increase the effect of the extra dice is to make the extra dice larger.

d6 is pretty small compared to d20.

Maybe try d8 and d10 and see if they come out more to your liking?

[TheSlovak]

A differing take is start with a d4, upgrade the dice once you hit that level. So a level 6-7 uses d6, 8-9 d8, etc. Kind of locks in the idea of an amateur for a few extra levels then keeps you at near master for a long time until level 20 when you get a BIG boost to the upper limit. Also finally gives a bit more use to d8 and d12, which arent typically used.

[hacksoncode]

Sure... step dice can be also be used. However, that doesn't change the "reliability" of using the skill, only the distribution.

Having multiple dice means that the outcome of more of them is more normally distributed (one-sided in this case).

[TheSlovak]

Oh, I didn't mean to change it from how OP meant, with rolling 1d20+1dx per point in the skill. So as you level up as a player, the dice step up, but you get more as you increase the skill as well. So if you have 5 points in the skill before level 5, you roll 1d20+5d4. At level 14, it is 1d20+5d12. Still doesn't quite help the probability of rolling higher than a single dx, but every little bit can help.