What are the practical limits of d20+mod vs DC?

Thread: What are the practical limits of d20+mod vs DC?

1. What are the practical limits of d20+mod vs DC?

What are the practical limits of using d20+mod versus DC? (I'm actually interested in the limits for any mechanic, but we need one to focus on, and the d20 version is a popular and easy one. Feel free to diverge.)

By practical limits, I mean that we can set mods and DCs however we want, but at some point it becomes rather silly. For example, if the greatest mods you can ever get, outside of leveling, are +0 or +1, then the luck of the d20 and the DC relative to your level, become the important factor. At the other extreme, sometimes we hear less than perfect satisfaction with d20+40 or other such high numbers, on the grounds that the high mods practically wipe out whole swaths of difficulties, making the roll irrelevant.

Naturally, there is some wiggle room by how one sets the DCs, and how the game scales. But I think we can put that down to mainly flavor. You can get a working model that doesn't scale, and a working one that scales rapidly. You can scale evenly or not. This will affect what you can do with the mods on the margins, but will it make any significant difference? (I could be wrong about this.) For any given category of mods, a certain amount may be presumed into the scaling. For example, a low-level 3E fighter with, somehow, a 22 Str is ahead of the curve, but not +6 ahead of it.

Assuming for a moment that the above is correct, then that means that the mods are where the action is. So what are the limits on those mods? If I have a system where you can get, say, a maximum mod of +3 from stats, +3 from magic, +5 from special abilities and situational modifiers, then what does that effectively leave me for skill (however represented in the system, but not counting scaling/level)? I'm already up to +11. If we go +4 for skill, then that means a maxed out character is at d20+15 versus an appropriate DC. Though granted, "situational modifiers" and other things that won't always be present would presumably be the interesting game play space.

Finally, I ask because I'm interested in how a game would feel if you managed to take out any scaling aspect from the mod categories, but kept some of the flavor as contrained bonuses. For example, a D&D fighter would be presumed to get a certain amount of attack bonus from "strength", but "being above average strength" would be more of a trait that granted a small but set bonus. And yes, I am thinking about the nature of Basic D&D as I write this.

2. In standard d20 rulesets, you quickly end up with a situation where only specialists can accomplish certain tasks, or where specialists never fail.

The lock an average merchant uses on his strongbox is either so good that it requires magic or a super-human thief to pop it open -- and a regular thief of average level will never open it without a new mechanic, like taking 20 -- or it's set at a level where a regular thief has a shot at doing it, but a higher level thief can walk right past it without slowing down.

Skill points, and thus DCs, ascending ever upward is one of the things I really don't love about d20. Either the rate of advancement needs to be slowed way down, or another system needs to go in its place.

3. Yes, the d20 skills mechanic isn't perfect. I find that a lot of people who enjoy RPGs don't actually play all that many types of RPGs. Some do, but most find one or two systems that works for them and then they tweak their system to whatever they're doing. You'll see that the d20 system is what it is, and it works great for that, but if you're looking for a more 'realistic' skill system, or even one that scales a little better it's difficult to use the same mechanic as d20 uses for combat.

What I would suggest is that you use 3d6 for your skills, plus one for every five points of skill points your character has in a skill. If your character has 8 points, he gets 4d6 to roll, count successes (6 and 5s), and use that to determine degree of success. A DC of 10 requires one, a DC of 12 requires two, and DC 14 requires three, so on and so on.

of course, if you were to do that, why not just design your own game? Take a look at FUDGE/Fudge

4. In the effort to keep the OP moderately short, I have once again been unclear.

Originally Posted by lulzapalooza
Yes, the d20 skills mechanic isn't perfect.
Having played many different systems, I can attest that no mechanic is perfect. This isn't about perfection. This is about the practical, workable, every-day limits of given mechanics, and what those limits do to feel. Scaling complicates the question, but it isn't the question. (That is, for any given system, you'll need to factor out the effects of scaling to see the practical limits.)

I think it is granted that mods ranging from +0 to +1 is too shallow. I think most people will agree that mods ranging from +0 to +50 might be a bit extreme. So what kind of range can you have? And how much can you divide that range into useful categories (magic, skill, etc.) before it gets overwhelmed?

5. Originally Posted by Crazy Jerome
What are the practical limits of using d20+mod versus DC?

10 character levels, IMO. When stretched to 20 levels it wears thin round the edges and once you try and stretch it to 30 or 40 or more, you're forced to create even more patches than the 20 level version already had to use. When they went from 10 to 20, they might have been wise to use a 30-sided die.

6. The expected value of d20+X = 10.5 + X.

Therefore, DC - 10.5 is roughly comparable to X. Let's call that value D.

I would say that the game works best when D is within +5 or -5 of X, giving a 25% to 75% chance of success.

So the DC of an action should be between 5.5 and 15.5 points higher than the mod.

7. Originally Posted by Crazy Jerome
I think it is granted that mods ranging from +0 to +1 is too shallow. I think most people will agree that mods ranging from +0 to +50 might be a bit extreme. So what kind of range can you have? And how much can you divide that range into useful categories (magic, skill, etc.) before it gets overwhelmed?
No matter how you cut the pie charts a d20+x is always going to equal something that doesn't scale all that well. It's not necessarily a bad thing, just an artifact of the way the d20 system works.

EDIT: I also want to mention how arcane the idea of 'scaling' is. I understand you to mean that you'd like the skills of a level one character to be closer to the skills of a level 10 or 15 level character? Making the differences more like comparing apples and oranges and less like comparing your second-uncle to Zeus?

8. Originally Posted by lulzapalooza
EDIT: I also want to mention how arcane the idea of 'scaling' is. I understand you to mean that you'd like the skills of a level one character to be closer to the skills of a level 10 or 15 level character? Making the differences more like comparing apples and oranges and less like comparing your second-uncle to Zeus?
No, what I mean is that ultimately the scaling doesn't matter on this question. I'm neutral on scaling. Not that is has no effects on feel, but that the effects are different than the ones I'm interested in. I only bring it up because so many of the d20 systems have scaling all tangled up with the mods, which confuses the issue.

9. As you know I've been bubbling away for some time tinkering and slowly developing my own system (I have a really neat twist on the DC mechanic but that is for a different thread and time).

I kind of figure it is like this:

Take a particular skill, it does not matter which one because you want the following to be universal for all skills, whether it is Knowledge, Perception, Athletics or Attacking with a sword or Casting a spell.

Novice
The novice who has no particular capacity, ability (or disability) for the skill has a modifier of +0. This makes sense in that the 0 neatly represents a non-negative, non-positive number/modifier. As such, the limits of their capacity is a DC 20. As such, if any task is within the realms of capacity of the completely unskilled, the DC should be 20 or lower. In addition, a DC of 1 or lower is defined as being routine for even a novice.

Master
Now lets go to the other end of the spectrum, to the master. The master can accomplish what is beyond the novice as a matter of routine. Numerically, this indicates a modifier of +20 or greater. Lets assume though that a +20 by definition is of a level of mastery (even if you can have grand masters or legendary use of the skill in question that may go beyond this +20 modifier). As such, a DC of 40 is at the limits of a master. Anything beyond that is of a difficulty that even a master would consider unachievable by reasonable means.

Proficiency
Now the interesting question becomes where you then set someone who is not only familiar with a skill, but proficient. Is someone proficient, barely above the novice (modifier +2)? Is someone proficient highly differentiated from the novice (modifier +10)? Where you set proficiency sets the "curve" of your modifiers. Now my own opinion (and my experience from playing international level pool) is that someone who is proficient, and someone who is a master can accomplish somewhat similar things. The difference between them is the consistency with which the master can produce these high results. As such my inclination would be to try and raise someone proficient to as high a level as possible (to about +8 to +10).

The beauty of this is that it also representative of the fact that a novice's inability can be advanced to proficiency quite quickly (proficiency can be achieved at 1st level) but that mastery takes far longer (thus giving the "curve" I'm talking about).

Note that such a way of looking at things is absolute rather than relative. I prefer a more universal absolute DC system that mirrors a set of reasonable expectations to one relative and less directly informative.

Modifiers
The interesting question I have now is looking at two polar uses of the DC skill system. What do you do with a skill that is almost purely about physical or mental capacity (almost completely reliant on the ability modifier) and one that is almost all about training where the ability modifier has a little effect (such as the most esoteric knowledge)? What things go into the modifier of such skills? What things go onto a modifier?

I think the best way of dealing with this, and staying within the system is to break every modifier down into 5 things. I'll use the athletic pursuit of swimming as an example:

- Ability: The ability modifier will always have an effect. Strength would be the main attribute here.
- General Experience and Capacity: This refers to how good the character is athletically in a general sense. Gross motor skills are the order of the day here.
- Specific Experience or Capacity: This refers to whether the character has any particular capacity in swimming versus other athletic pursuits such as climbing or running or jumping.
- Equipment: This refers to objects or things that may assist such as flippers or buoyancy apparel but also to things that may hinder such as armor or bulkier apparel. [For a melee skill, a masterwork sword might provide a +3 bonus where as a dull used sword may provide a -1 penalty or worse.]
All of the above do not stack within themselves (you may remember this CJ from the other thread). A +3 general bonus from one general source and a +2 general bonus from a different source do not stack. [Edit: Sorry, Equipment modifiers should stack as well as the special bonuses below]

- Special: This is your circumstance bonus, magical bonus, or holy bonus or what have you. All of these "special" bonuses do stack. The trick is that Special bonuses are usually derived from transitory rather than permanent effects. This is the best way to have variety, while keeping things balanced and having the capacity to strictly enforce modifier caps on each of these five modifier sources.

Hopefully there are some ideas in there that can get you thinking.

Best Regards
Herremann the Wise

10. Originally Posted by GSHamster
The expected value of d20+X = 10.5 + X.

Therefore, DC - 10.5 is roughly comparable to X. Let's call that value D.

I would say that the game works best when D is within +5 or -5 of X, giving a 25% to 75% chance of success.

So the DC of an action should be between 5.5 and 15.5 points higher than the mod.
That tracks pretty consistently with what I have observed in Hero System and GURPS. Using the 3d6 versus a DC, the mods can rarely exceed -3 to +3. In Hero, this is even baked into some of the standard numbers, where 11 is considered the baseline, and 8 and 14 are the standard outer edges, representing success chances of 25%, 65%, and 90%.

I do like my baseline somewhere closer to the 2/3 success mark, though I understand people have argued for 50% to 75% or so.