UPDATE: We have modified our table to more closely reflect the by-the-book numbers at higher levels.

One of the things we’re doing for our Labyrinth Lord-based homebrew game is to convert the thief skills over to a d12 roll-under mechanic from the standard percentile system. I used a d6-based scheme for my White Box Thievery system, but I prefer d12 here because we’ve got more potential levels to worry about and the finer progression of the d12 allows us to scale up more skills per level.

Currently, we’re increasing four skills per level advance. Also, the starting rates of most skills are better than 1st level by the book, but the progression is slower in most cases, meaning the thief is better in the earlier levels but slowly falls behind.


Pick Locks Find or Remove Traps Pick Pockets Move Silently Climb Walls Hide in Shadows Hear Noise Read Lang Cast Scroll Spells
1 4 3 4 3 9 3 3
2 4 4 5 4 9 3 4
3 5 4 5 4 10 4 4 3
4 5 5 6 5 10 4 5 3
5 6 5 6 5 11 5 5 4
6 6 5 7 6 11 5 6 4 3
7 7 6 7 6 11 6 6 5 3
8 7 6 8 6 12 6 7 5 4
9 8 7 8 7 12 6 7 6 4
10 8 7 9 7 12 7 8 6 5
11 9 8 9 8 12 7 8 7 5
12 9 8 10 8 13 8 8 7 6

In play, we will probably make use of a lot of modifiers depending upon situation. We will also specify the standard chances of non-thief characters (on d6) when attempting these things, though not all of them will be possible for non-thieves.

Magical languages can be read at half the chance (round down) of reading normal languages.

Casting spells from scrolls applies to magic-user and illusionist scrolls and the spell level is deducted from the chance to cast. Failure by rolling triple the target number or greater indicates that the spell has been erased from the scroll, otherwise failure simply means that it did not trigger and can be tried again. Failure by rolling a 12 probably indicates catastrophic and spectacular failure, however.

This has not been used in play yet, so feedback would be particularly welcome at this point.

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17 Comments to “D12 Thief Skills”

  1. Timeshadows says:

    So the chance to cast a 1st-Level spell from a scroll is really a 2 or less at L6 then, etc.?

    • Kilgore says:

      Yes, as I’ve got it now. We haven’t quite worked out the odds on either read or cast yet, and we haven’t decided if a successful read magic needs to be done before a casting attempt, either.

      But right now, yes, a 6th-level thief would have to roll a 2 or lower on a d12 to cast a first-level spell from the scroll. If it fails, he can try again unless the spell was ruined by rolling greater than 6.

      • Kilgore says:

        I also caught an error in the progression for [Hear Noise] and am posting an corrected version now.

        • Timeshadows says:

          So that’ll give a 41% chance for a L12 Thief to cast a 1st-Level spell from a scoll.
          –May I ask what the base percentages are in the source material you are drawing this from?

          • Kilgore says:

            Actually, I am not pulling the numbers for casting from anywhere. I added that particular category myself.

            Are you thinking the chances are too low? I would not argue at this point.

          • Timeshadows says:

            AD&D has a 10th Level Thief with a 75% chance to cast all scrolls (except for Clerical), with an unstated chance based on the spell level of Reversing the intended operation of the spell.

            Without taking that into account, we are looking at a 7.5% per Thief Level to successfully cast a scroll spell.

            I can see where you are getting the n in 12 chance, as 1/12th = 8%
            –I suppose you are using a 7% chance failure rate per spell level, or something like that?

          • Kilgore says:

            To be honest, I just picked a starting point and progression that “seemed right.”

            I didn’t remember that AD&D success rates were that high, though. I knew my numbers were a little lower.

            My current numbers have a 33% chance for a 10th-level thief casting a 1st level spell.

  2. Timeshadows says:

    Well, man, you are pretty close on that guestimation, save that you are starting it later than the extrapolation that back-engineering from 10th would suggest, but hey — that’s just a matter of taste. 🙂

    • Kilgore says:

      Wait, I just looked at my notes and realized I changed my number to reflect “level over 1st” but had forgotten. I’m not exactly sure why I did that, but I think it might have been because all skills except climbing started at 3-in-12 at the time. That is no longer the case.

      So the chance for a 10-level thief to cast a 1st level scroll spell would be [5-in-12 (42%)].

      Now I need to think about this a bit. I’ll have to grab my PHB and check out the AD&D scheme.

      EDIT: Gaaaahhh!!! I’m looking at like four different versions of the table and keep screwing up.

  3. Timeshadows says:

    I’ll be back on in a bit to see what you’re up to.

    In any case, I think the overall effect if pretty cool. 🙂

  4. Erin says:

    Good conversion, but is there any reason you wouldn’t just base it on a d20? It would make the modifiers more scalable. In my experience, when you say “+1” most players unconsciously assume +5%, not +8% (which is +1 on the d12). Not a big deal if it’s well-defined, but I’d personally try to use a more consistent convention.

  5. Kilgore says:

    Good conversion, but is there any reason you wouldn’t just base it on a d20?

    Yes, specifically because all the skill-like “checks” for non-thieves are d6-based. By going with d12, they can match up.

    • Erin says:

      Makes sense. Based on that, though, I’d keep the 1d6 for thieves as well, but let them roll 2d6 and take the best result.

      Possible benefits: if both rolls succeed, treat as a critical success; if both rolls fail, treat as critical failure (e.g., trap goes off, pick pocket attempt is noticed, lockpick breaks).

      • Kilgore says:

        I just saw something about the “roll 2d6 and keep the best result” method somewhere and think it’s a great idea. However, it doesn’t allow for graduated progression as easily. I like the idea that a 3-in-12 chance is also a 1.5-in-6 chance.

        Plus the d12 doesn’t get used enough. I’m thinking of converting combat to d12. (Okay, just kidding on that last one…)

        • Erin says:

          Don’t be hasty – I completely agree that the d12 is unfairly ignored. In fact, here’s a secret: That’s the only reason Chimera initiative uses 1d12. Really.

          But, in a last-ditch effort to play devil’s advocate, you could still use 1d6 for thieves, but maybe they don’t get the 2nd die until 4th-level (or some other appropriate cutoff).

          I do hear you about granularity of the d12, though. BTW, any thought about using 2d6 against your table above? You’d be dealing with a bell curve (average 7), which would make it harder to be a thief at low levels, but easier at high levels. Just a thought…

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