Nuanced Advantage and Disadvantage in Basic DnD

One last post, this one courtesy of a request by Emily Smirle over on the SJG Forums, where a fairly civil discussion of the new edition is taking place.

States of Relative Advantage


Something that’s very clear in the rules, is that if you find yourself in a situation with both advantage and disadvantage, they cancel out and you just roll 1d20. If you have multiple sources of advantage, you only get it once. And if you have multiple sources of advantage and disadvantage, they cancel out and you just roll 1d20.

That’s a good, simple way of handling things. But it’s not the only way. Digging into some of the questions in Emily’s post let me to hit AnyDice again, and once again I found something interesting.

How much advantage can you have


There’s a spectrum of potential here, and in order to take advantage of it (see what I did there?), we’re going to have to pick up a third die. Sometimes. Not always.

What you say? 

Well, consider the possibilities:

Pure Advantage: Whether it’s one case or many, the odds are ever in your favor. You have only advantage stacked up on this task. (Roll 2d20, pick the highest)

Mostly Advantaged: You have multiple cases of advantage, and they outnumber cases of disadvantage, of which you have at least one. (Roll 2d20, pick the lowest; then roll 1d20. Take the highest of those two numbers)

Equally Advantaged and Disadvantaged: You have a case where you’ve got both advantage and disadvantage, and they cancel each other out. (Roll 3d20, take the middle one)

Neither Advantaged nor Disadvantaged: A pure task roll. Grab your d20 and have at ’em! (Roll 1d20)

Mostly Disadvantaged: The opposite number of Mostly Advantaged; you might have two cases of disadvantage and one of advantage, or seven disadvantaged states and three advantaged ones. Doesn’t matter. If disadvantage outnumbers advantage, you’re here. (Roll 2d20, take the highest; Roll 1d20 again, and take the lower of the two).

Pure Disadvantage: Sucks to be you, but there you go. (Roll 2d20, pick the lowest)

If you’re willing to roll up to three dice for a given test, you can get some nice shades of grey going on in the distributions.

AnyDice Me

The chart shows the level of distinction possible with the possibilities outlined above. 


Pure advantage and disadvantage lie appropriately on the upper and lower bound of success probability relative to a flat 1d20 roll. 

The Mostly Advantaged and Mostly Disadvantaged columns are better than a flat roll, but not as good (or bad) as the pure versions of either one.

And the balanced Ad/Disad version looks like an understated version of 3d6, but not with more than (eyeballing it) about a +/-1 or 2.

Parting Shot
By this time, some of you are shouting “just play the fracking game!” instead of tweaking dice mechanics. There’s truth to that, but to first estimation. the Basic DnD rule book will play more or less like the Swords and Wizardry game I play in monthly. Relatively low bonuses, and perhaps a simpler execution of some things.

But the question Emily asked got me curious, and the answers were once again surprising. If you’re willing to put up with picking up as many as three dice, and also paying attention to order of operations (both perhaps unwanted complexity) you can get some very interesting nuance to the tests.

The interesting thing to me about the intermediate steps is the behavior of the criticals. Just looking at the odds of rolling a 20, the nice thing about having any amount of disadvantage is that it knocks your odds of rolling a 20 to either “basically equal to a flat roll” or “significantly lower.” 

Being mostly advantaged gives you essentially the same chance of rolling 18-20 as a flat roll. But you start to pick up a +1 immediately and rapid hit something like +3, before tapering off to the same success chances as a flat roll at the upper end. That is, you’re not any more likely to do hard things (due to the small amount of disadvantage you carry), but are more likely to succeed (due to advantage).

The balanced Ad/Disad state is also interesting. You’re less likely to crit, and less likely to miss. Basically, it’s a very mild “bell” curve (it doesn’t look like a bell at all) that steers results away from the extremes.

The possibilities here are nuanced, it’s true, but if you’re willing to put up with a bit more complexity in how you do the rolling, you can take the “just don’t worry about it” out of the combination of advantage and disadvantage to good effect.

Thanks to Emily for steering me to look at this. It was fun.