We were talking about the consequences of taking wounds, or having had your Stress Points worn down. Just brainstorming in an idle fashion, tossing out ideas, and someone, I think Peter, mentioned that if things were in a really bad way, that you could pick up Stacked Disadvantage.
Hmm, we said. What would that be? Well, probably taking the lowest result of more than 2d20. But does that look interesting compared to regular Advantage/Disadvantage?
Turns out it does.
Turns out it does.
You can see from the probability of exceeding a given difficulty number that the Stacked Disadvantage is significantly less favorable than picking the lowest of 2d20, and the Tim Shorts level approaches the actual probability of Tim rolling higher than a 1 on any important combat task.
So that’s one way to look at it. Another is to look at the equivalent probabilities of meeting or beating a target number – basically take all the modifiers that go on either side of the equation and make it 1d20>N. So if you normally roll 1d20+5 vs. AC 16, this becomes 1d20 greater than or equal to 11 (which should be, and is, a 50% probability).
That chart shows what simple mental calculation shows too: the odds of rolling a good roll with Stacked Disadvantage are really bad.
Finally, another simple way to get a feel for what’s going on here is a risk-based one. What number can you expect to roll under X percent of the time? That’s a way of asking how concentrated towards the bottom of the target number range the dice will be, and as you can see, it’s pretty ugly.
Again, as you expect, with a straight-up roll, half the time you’ll roll 10 or less, and 90% of the time you’ll roll 18 or less. That’s a boring flat distribution, but that’s 1d20 for you.
Stacked Disadvantage has 90% of your rolls being 11 or less. And 19 times out of 20 your best roll can only be a 12. Note that rolling 1d20+5 vs AC 16 only really requires an 11, but that means Stacked Disadvantage takes that chance to pretty low – about 12% in fact.
One last way to look at this is that given Disadvantage, Stacked Disadvantage, or Tim Shorts, what’s the equivalent penalty?
This method of looking at it has its limits. Your odds of rolling (say) a 20 are only 5% with 1d20, and saying that you are at -1 because your success chances go from 5% to 0.012% really, really understates how unlikely the die is to come up 20 on all three (or four, if you’re Tim) dice. But the depth and breadth of the valley of doom is illustrative of how deep in the trouble pool you are.
As much fun as it is to bust on Tim for the frequency of his rolling a 1 at exactly the wrong time, in reality, going to the fourth d20 doesn’t really buy you much. Unless the player is attempting a ridiculously easy task – rolling with proficiency and/or expertise and an attribute bonus against a DC 10 or lower target (so net difficulties of 3-5), there’s so little probability of success that the GM might as well say “nope, can’t roll.” Also, the difference between lowest of 3d20 and 4d20 isn’t that much: never more than the equivalent of another -2 tossed on top of everything else.
So I’d leave the “lowest of 4d20 “level behind, but Stacked Advantage and Disadvantage may well find their way into my stable of things to use when GMing 5e.
Oh: I don’t expect I’m the only one to think of this (and in fact, Peter was the one that did), but it seemed cool enough to write up anyway.
Follow-up and Commentary
Well, this looks like it’s going to be a popular post, or perhaps notorious. I’m getting a lot of feedback, especially on Reddit, but it’s good stuff.
Also is the stacked dis/adv something that the DM holds onto until times where it is called for(kind of like handing out inspiration) or is it something that is always in play? If it is always in play I think it can really break the game once you start building characters to take advantage of the rule. Right of the top of my head I could build a straight up human variant barbarian who would have stacked advantage on almost, every attack. I think this is the reason WotC decided to not make dis/adv stackable right out of the gates.
Yes, quite – I’d not considered that one fully. That point about a double-stack adv/disadv by character design is a good one. My mental image was that this sort of thing would be only applied based on conditions. So that (for example) if you were, um, grappled AND on ice, yeah, that’s doubly sucky.