d20 skill-check hack

As noted here:
Where d20 breaks down is when it shifts to non-combat rolls where the entire task (skill) is handled with a single, linear-odds roll.
Here’s how to fix that.
There’s a little known optional combat rule that states that people can choose to ‘roll’ their AC every round. Basically, you don’t have a Base 10 AC… figure out whatever you’ve got over 10, call that your “AC Bonus”, and add that to a d20 roll every time you’re attacked.
I doubt anyone does that — hell, I doubt anyone knows it’s there — but look in the DMG.
ANYWAY: while I don’t recommend it for combat necessarily, I think it would be useful for Skill Checks. Many of these are Opposed Rolls anyway — this little house-rule would make all Skill checks opposed.
Find the current DC for a skill. Subtract 10. Whatever’s left over is the DC Bonus. When someone tries to do something to overcome that challenge, the GM rolls a d20 and adds that DC bonus.
What does this do? Two main things.
1. Creates a pyamidal instead of linear success curve. In the case of a Thief with Open Locks +15 vs. a Lock with a DC bonus of +15 (formerly a DC 25 lock):
00.25% You Crit succeed, it crit fails.
02.50% You Crit, it fails
49.5% You succeed, it fails (or, you tie each other)
44.75% You fail, it succeeds.
02.50% You fail, it crit succeeds
00.25% You crit fail, it crit succeeds
00.25% Mutual Fumble
It’s a pyramid curve, but it’s a curve.
2. Removes instances of “Ugh… I got a 19… I know that d20 modules always set the DC’s in five-point increments on everything, so I’ll spend an Action Dice to give me a boost… worse case scenario, I get to a 20, and maybe I’ll get to the 25 break point.” (Particularly annoying on Gather Information charts, when adding the AD will almost certainly glean more info)… If the DC’s are d20+5, d20+10, d20+15, et cetera instead of 15, 20, 25… there wouldn’t be those artifical ‘rungs’ in the DCs to shoot for… that d20+5 DC might be, on your try, a net DC 6 all the way up to a net DC 25… every NPC you talk to is talkative in different ways, after all.

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5 Replies to “d20 skill-check hack”

  1. It has some other impacts, too, which I talked about briefly in my first (and only, so far) post on 20′ x 20′ Room.
    Bringing in a curve (even a sharp 2 die curve) tends to bring down the value both of low skills and of high skills, as the extremes of rolls become less common. Low skills will succeed far less often. igh skills will dominate sooner (i.e., being 10 points better is nearly as good as being 15 points better), so why bother with all the extra skill?
    The mechanic strongly encourages balanced, well-rounded characters with as many skills as possible kept right where they match contesting skills, with any luck around 1-2 points ahead.
    It also dramatically increases the uncertainty of any roll (double the variance, as two dice are rolled not one), and so will reduce the certainty of any action done in the at-risk range (say, when you’re within around 8-10 points of the opposing value) and dramatically increase the certainty outside it. As PCs rarely get to do anything that far below their skill in critical moments, the result may well be far more cautious characters, as the odds are now well against them taking long-shot chances. Linear distributions help a character who’s on the short end of the odds, and D&D PCs are often there.
    It’s a particular problem in combat, as it makes a well-kitted-out “tank” character all but unhittable, since more AC can be bought for money (armor, shield, misc item) than to-hit (weapon).

  2. I agree on all points except for the last bit about combat… while it’s true that you can get AC-boosting stuff easily and can’t do the same with weapons until you get magic stuff, by contrast the DnD characters automatically increase their to-hit range as they level up, while their ‘natural’ AC rarely changes.
    not that I’m advocating this mechanic during combat in any case — too much rolling.

  3. Well, my worry re: AC is that one can get that up high via cash (equipment, mundane and magical) or spells many, many levels before anyone can manage to hit you, since to-hit is limited by BAB development. Eventually, BAB will catch up and probably pass AC (excepting true tanks like a plate mailed dwarf), but there’s a serious time mismatch possible if someone focuses on AC.
    The big problem of needing extra bonus to his PC A but that bonus making you overpowering vs. PC B is one D&D tries to balance with its level-based caps on abilities, but AC is the most obvious exception. Bell-curving the die rolls would make the current mismatch dramatically worse for mid-level (rich enough to afford great armor, not enough XP to have great BAB) gaming.

  4. Definitely — the opposed roll thing isn’t something I’d probably ever use in combat for this and other reasons. For skills, I can see the benefit of it… especially if, for things like picking locks, the PC can take 20 but the lock can’t 🙂

  5. Reading back here, so bear with me:
    That optional combat rule in the DMG — it’s in 3.0? You know, I started glazing over when reading that book initially, and I’ve been running games almost three years now. What section is it in? My curiosity is piqued, along with your idea on skills.

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