Roll xd6 under ability: yet another D&D skill system

I promise: this is the last skill system for OD&D / BX D&D I write about this year!

(Not quite the first one, though....)

So, here is the thief table skill from BX, with one very good and easy solution for people that prefer a more unified skill table, from Tales of the Grotesque and Dungeonesque (source):

This solution is not only easy and elegant, but also answers the question "what about other classes" (answer: 1-in-6 for everything), and makes the thief better than everybody in this regard, which is essential. LotFP does something similar.

There is at least one different solution it you want things to be a bit fiddlier.

James V West (Doomslakers!) posted this to G+ a few hours ago (from D&D Companion set, book 1, page 9; click to enlarge):

It is an interesting bit, and contains a variation of Moldvay's "there is always a chance". Here is the relevant part:

But would that work with thieves' abilities? Let us try with 4d6 (the numbers are form anydice.com):

Roll	%
4	0.08
5	0.39
6	1.16
7	2.70
8	5.40
9	9.72
10	15.90
11	23.92
12	33.56
13	44.37
14	55.63
15	66.44
16	76.08
17	84.10
18	90.28
19	94.60
20	97.30
21	98.84
22	99.61
23	99.92
24	100.00

You have 15.90% chance of rolling 10 or less with 4d6. Try this: add thief level to any ability, Assuming the thief has 10 in any given ability, you would have to roll under 10+level with 4d6 to succeed. These would be your chances:

Level	%
1	23.92
2	33.56
3	44.37
4	55.63
5	66.44
6	76.08
7	84.10
8	90.28
9	94.60
10	97.30
11	98.84
12	99.61
13	99.92
14	100.00

Close enough? The thief becomes a bit more competent overall, which isn't a bad thing IMO. The chances are even better if the thief has a high ability score. You might use Dexterity for stealth and picking locks and Wisdom for hearing noises, thus "customizing" each thief without needing different tables. Or just use 10+level for everything if you want things to be simpler.

The problem is that 100% there; you see, there is always a chance of failure in the original rules, and I kinda like that. What if we chose a single one of the die to explode, i.e, add another die if you roll a 6? This is probably too fiddly, but the results are quite pleasing: a level 10 thief with Dexterity 15 would still fail 2% of the time, and a level 14 thief with Dexterity 18 would still have one chance in a thousand of failing (there is always a chance!).

(Level)	Roll	%
	4	0.08
	5	0.39
	6	1.16
	7	2.70
	8	5.40
	9	9.65
	10	15.60
1	11	23.21
2	12	32.21
3	13	42.12
4	14	52.21
5	15	61.79
6	16	70.35
7	17	77.56
8	18	83.30
9	19	87.65
10	20	90.88
11	21	93.25
12	22	94.99
13	23	96.28
14	24	97.25
	25	98.00
	26	98.57
	27	99.00
	28	99.32
	29	99.56
	30	99.73
	31	99.85
	32	99.92

Even closer to BX! Compare it to the open locks progression. BTW, "the obvious solution is to just use open locks as a generic "chance to perform any thief skill" as you can see here (post #232).

This also "solves" climbing, by the way. Just use 2d6, since if is apparently easier than any other thief skill:

Roll	%
2	2.78
3	8.33
4	16.67
5	27.78
6	41.67
7	55.56
8	67.13
9	76.39
10	83.33
11	87.96
12	90.28
13	92.59
14	94.52
15	96.06
16	97.22
17	97.99
18	98.38
19	98.84
20	99.23
21	99.54
22	99.77
23	99.92
24	100.00

So, 2d6 for easy stuff, 3d6 for ordinary things, and 4d6 for specific skills such as picking locks, hearing noises, etc. 5d6 for truly legendary feats.

From then on, you can add a few skills to other classes, explore different abilities (maybe the strong fighter is a better climber than the thief at level 1 - now every point matters), add specialties (roll one less dice if the PC is an expert), mess around with fractions, and so on. Backstab? Got you covered.

Source - xkcd. Like you didn't know.

So, now I have, what, half a dozen skill systems for B/X? All because I wanted a single one... Yeah, I guess that is how it goes.