Riffing on 2d6: Reaction Rolls

I've started to take a real liking to 2d6 as a dice mechanic. For the longest time I didn't actually care for it, I was a fan of rolling a d20 for almost everything. But I've spent a lot of time thinking about the classic reaction roll in D&D (inspired in part by this post) and the longer it sat around in my brain, so more useful the probabilities created by 2d6 seemed to get. Here's how that reaction roll works abstractly, at least in most D&D-variants (B/X D&D, page B24 for example):

2d6	Outcome	Probability
2	really bad	2.78%
3-5	bad	25%
6-8	neutral	44.45%
9-11	good	25%
12	really good	2.78%

This has some nice properties. Obviously the "neutral" outcome is most likely which is probably just as well. After all, this is meant for a confrontation with a random pack of monsters who just popped around a corner. If both sides indeed "try to chat" that should probably lead to a temporary stalemate more often than not. Then there's a pretty decent chance for making "progress" in one direction or the other. I think that fits the "random negotiation" model again where both parties can usually feel that things are starting to slip before any actual stabbing occurs. Finally there's a pretty slim chance that things lead to immediate hostilities or immediate friendship. Neither of these should be very likely when you turn a corner and suddenly face a dozen kobolds: your side may be worried about being outnumbered, but their side should be worried about your big swords. So to me, this is just about perfect for monster reactions.

It's strange that Gary Gygax decided to mess with this for AD&D where reaction rolls are suddenly percentile-based. Here's what he (unenthusiastically in my opinion) proposes in the Dungeon Master's Guide (page 63), again abstracted a bit:

d%	Outcome	Probability
1-5	really bad	5%
6-25	bad	20%
26-45	neutral, negative bias	20%
46-55	neutral	10%
56-75	neutral, positive bias	20%
76-95	good	20%
96-100	really good	5%

What exactly are three versions of "neutral" good for except to complicate the table and to force the poor referee to be prepared for seven different outcomes to portray? Five different outcomes already enough of a workload! Also we get slightly increased chances for "really bad" and "really good" at the price of upping the total chance for "not sure yet" to 50% instead of 44.45%. That really only seems to lengthen the average time spent on the mechanic (negotiations take longer to conclude). As far as I am concerned, this is one of several cases where Gary was trying too hard to be "advanced" as it were.

If the point was to make the extreme outcomes more likely, he could have achieved a similar effect just by using different bins:

2d6	Outcome	Probability
2-3	really bad	8.34%
4-5	bad	19.44%
6-8	neutral	44.45%
9-10	good	19.44%
11-12	really good	8.34%

I am not sure if I am the first person to propose this? Maybe Gary even tried it but decided that 8.34% is too much? Who knows with these things...

Interestingly the reaction roll comes in two variants in OD&D. The "monster reaction" variant was actually an even simpler 2d6 roll with only three possible outcomes (Vol 3, page 12):

2d6	Outcome	Probability
2-5	bad	27.78%
6-8	neutral	44.45%
9-12	good	27.78%

This variant is also used in the Confusion spell (Vol 1, page 27). The variant with 5 outcomes (as above from B/X) was used only when recruiting monsters (Vol 1, page 12), not when encountering them.

Using the simpler OD&D table with three outcomes, there's yet another variant we could construct by attaching "special meaning" to rolling doubles. For each of the three outcomes there are two ways of rolling doubles: 1-1 and 2-2 for "really bad", 3-3 and 4-4 for "really neutral", 5-5 and 6-6 for "really good" as it were. It's easy to interpret "really bad" as "monsters attack" and "really good" as "monsters help" but what the heck does "really neutral" mean? Maybe that negotiations end right there and the monsters just decide to leave? Seems reasonable I guess. Opinions?

In terms of probabilities we now get something a bit more complicated to figure out, but it's not impossible. It is, however, a pain to put into a table because the "special outcomes" are not a contiguous range:

2d6	Outcome	Probability
2-5	really bad	5.56%
2-5	bad	22.22%
6-8	really neutral	5.56%
6-8	neutral	38.89%
9-12	really good	5.56%
9-12	good	22.22%

So for the "non-neutral" outcomes, that's also close to what Gary did with his AD&D reaction roll. On top of that it's pretty cute to make doubles meaningful, at least I find it fun.

I don't know if this turns anybody else on to 2d6 but I sure had fun writing it all up. There's more in my brain regarding 2d6, at least the "turn undead" mechanic and using 2d6 for skill checks. We'll see when I have the time to write them up. In the meantime, I'd love to hear your take on 2d6 in general and reaction rolls in particular.

Update 2014/12/11: Who would have thunk it, there are still more variants on the reaction roll! I noticed this earlier today when reading this post over at DHBoggs' fascinating blog. The version he gives comes from the "New Easy-to-Master Dungeons & Dragons Game" but it's also in the Rules Cyclopedia (page 93). Here's my reproduction with percentages inserted as I've done for the other versions above:

2d6	Outcome	Probability
2-3	really bad	8.34%
4-6	neutral, negative bias	33.33%
7-9	neutral	41.67%
10-11	neutral, positive bias	13.89%
12	really good	2.78%

Given the historical precedent discussed above, those asymmetric ranges are certainly strange: Monsters are now more likely to attack than to be cooperative! (Maybe that's just as well, after all the later versions of the game seem to encourage combat more anyway.) The AD&D idea of "bias" is back again, so there's a good chance (a 47.22% chance in fact!) that you'll roll on this table at least twice before getting a result (the rules recommend stopping after three such rolls). Note, however, that there's no longer a "good" and "bad" category, only the extreme outcomes are actually possible.

Now if you think this is a bad table for the reaction roll, think again. Think hard! Because I am about to show you an even worse one. If my brain is any indication, we simply repress things we find horrible even if we grow up with them. Case in point, I played a long-ish campaign using the Rules Cyclopedia back when it came out. I thought I knew those rules pretty well. But when I first wrote this post, I couldn't remember this whacky reaction roll table at all. I must have repressed it!

But now open your 1983 Mentzer Basic Set, Dungeon Masters Rulebook, and turn to page 22. Yes, look at that triply-nested monstrosity. I won't even type it up, I'll just use a scan:

I know I certainly repressed that one. There's literally no record of this anywhere in my brain. And yet that's the D&D I grew up with, the D&D I played forever and ever before getting the Rules Cyclopedia. Did you repress it too? In protest, I'll leave the analysis of this table to someone else.