Two scouts or one: the effect of skill check rules (reference to dndblog.powerblogs.com)

So, the following issue has come up: the party has one rogue, Acavel, who's the best hider and silent mover (understandably). Barik, a ranger, could pour his skill points into hiding and moving silently, and together with a cloak of elvenkind or armor of shadows, could be as good at hiding, and a few ranks lower at moving silently. On the other hand, the one rogue could use the armor instead, and be _really_ good at hiding. So do we want one character to sneak around, recon, etc., or two?

Tactically, there's a lot to be said for having a team of two instead of one. If they find something, one can report back while the other keeps an eye on the situation; if they run into trouble, one can hold off the hordes while the other gets help, or at least the two can support each other in an organized retreat. Or, they could go off into different directions, surrounding an opponent or covering more area faster.

Here's the problem: suppose the two of them are headed down the corridor, and something might hear them. How's that get resolved? The way I interpret the rules (at least at first), they each roll their Move Silently checks, and the something rolls its Listen check, and if it gets a higher score than one of them, they're rumbled.

Probability-wise, this is quite a bit worse than one of them going alone, even if they have the same skill. In that case, it's the same probability as if the one going alone rolled his Move Silently, and Evil DM (tm), after seeing that roll was too good, said "naw, don't like that...roll again, see if you fail this time." To put it even more mathematically, if either scout had an M in N chance of being undetected (i.e., 1 in 2=50%), the two together have an M squared in N squared chance (25%, in the previous parenthetical).

That's a pretty vicious penalty. So PCs adopting the two-scout strategy should reconsider -- although a two-watchman strategy when you're camped out makes a whole lot of sense.

Unless you're a diehard fan of D&D rules trivia, stop reading now. The last paragraph was the most useful comment you're going to get out of this.

Group skill checks are one of the times when the situation for a group of NPCs need not be symmetrical to that of a group of PCs, although it's quite unclear. The DMG's section on Skill Checks (3.5e, p.30) indicates that for "influencing one person, creature, or group" or to "perceive one sound or sight", the "DM decides if NPCs are acting as individuals or as a group." How or if this applies in opposed checks is not at all clear; I go into detail about some possible schemes at the bottom of this post, below the line of asterisks. Don't read that unless even the other diehard D&D trivia fans think you're a freak. In the meantime, let's assume that this grouping thing doesn't apply; in opposed checks, every PC rolls and every NPC rolls, and each Spotter/Listener detects all the Hiders/Movers who scored less than they did. This makes it awfully hard for anyone to sneak past a group, and can generate boatloads of die rolls, but at least it's "fair".

How hard is "awfully hard"? Consider a "commando team" of rangers, sneaking up on a camp of orcs all gathered by the campfire singing "Kum-bay-ya". Let's say there's 5 rangers, around 9th level. Counting their +4 from dexterity and +2 for circumstances and the max +12 skill ranks, they're +18 on both Hide and Move Silently checks. These are just a score of grunt orcs, and let's give them a -2 for circumstances, so they're +0 on both the Spot and Listen checks. Unless a ranger rolls a 1 and an orc rolls a 20, the rangers won't get discovered.

The odds of one orc rolling a 20 and one ranger rolling a 1 are 1/400 (0.25%). But the chance of at least one of the 20 orcs rolling a 20 and one of the rangers rolling a 1 are 14.47%. And that's just the chance of the rangers being spotted. The chances of them being spotted _or_ heard are 26.9%, just over 1 in 4.

Here's a more typical example. Suppose a single rogue has a +10 to their Move Silently roll, and he or she rolls a 10 while trying to sneak pass a room. If it's got one guard in it, with a +6 Listen check, the rogue has a 70% chance the guard won't roll the 15 or more he needs. Change the number of guards to 4, and that chance drops to 24%. That seems low to me -- although if the "opposed check" were a tug-of-war, maybe that'd be about right. One way to try to fix this would be to give the guards all a -2 circumstance penalty (because they're distracting to each other) -- then the chance of the rogue's success improves some, up to 40%.

Or we could pretend three of the guards are really doing "aid another" attempts for the first one's listen check -- I don't even know how that would change the probabilities, but it could make things worse, not better. Or maybe after the second guard, the other two don't really help any, and can't make checks. And if that isn't complicated enough, how do we treat the inverse problem of a group trying not to be detected? Do we not have people after the first two make checks, because they don't contribute to the silence?

The simplest alternative system would be that in any opposed check, each side only makes one roll: the best Spotter/Listener rolls vs. the worst Hider/Mover, for example. But that ignores the contribution (or lack thereof) of the rest of the people entirely. Why is it always Hawkeye that catches the goblins? And does he see all the goblins, or just Klompy? What if some of the quieter goblins were coming from the other side? Do we treat them as a separate group? Oh geez, I thought this was the problem we were trying to simplify away...

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[This is the consideration of "asymmetrical" opposed checks, where a group of NPCs is treated differently from a group of PCs. If you haven't been riveted by the post so far, you're really going to despise the time you'd be wasting if you read this. You've been warned.]

The examples in the DMG indicate that a PC would get one check to spot a group of NPCs at a distance [Note: it's not clear if this is an opposed check, but it seems not], but that a PC Moving Silently would face the Listen checks of every NPC in a group. But what about a group of PCs Moving Silently? Do the NPCs get one number to beat, or the worst of two? There isn't a clear example I can find in the DMG of opposed checks where the NPCs are treated as a group -- would that mean they make one roll, or that they only have to oppose one roll, or that NPCs each make their own roll in opposed checks, and are never treated as a group? The third case makes the most sense, that I talked about above, although the first one isn't completely crazy. The second one is in fact completely crazy, and I'm worried about my own mental health just as a result of thinking about it.

The first case isn't symmetric, but it's not entirely unbalanced: if a group of NPCs rolls once for the whole group, that means they'd be harder for an individual to spot that a group of PCs (since they'd only have to succeed once, while each PC in a group would have to succeed), but they'd be worse at spotting an individual (since they've only got one chance to succeed, while the PCs would have a chance each.) If a group of NPCs and a group of PCs try to sneak past one another, there's still a good chance they'll run into each other, since the PCs have a lot of chances for high Spot/Listens, but just as many chances for low Hide/Moves. The chance would be considerably reduced from the "everyone rolls against everyone" scheme, however. The PCs would be wise to have multiple people on watch, but only send one out for scouting reports, so they're not fighting the probabilities.

The other asymmetric case is that the group of NPCs only opposes one roll (that is, all the NPCs make a check against one roll for the PCs.) This seems pretty antithetical to the idea of D&D, since the NPCs are being treated more individually than the actual characters with individual free wills, but let's put that aside for a moment just to consider this silly case for academic purposes. Then the roles are reversed, and the only interesting twist is how to decide what the bonus on the PC roll is: is it the bonus of the most skilled PC, the least skilled, an average, or is it different for different skills? (A group of generic NPCs are pretty close to the same skill level, so I didn't mention this for the previous case.) No matter the bonus selection mechanism, the PCs don't gain anything by having more than one night watchman; in fact, if the PC bonus is anything but "same as most skilled PC", it actually hurts them to have more than one! On the other hand, it doesn't hurt them to send out several scouts -- if several PCs have the same skill bonus, there's no penalty for numbers. Again, opposing groups (PCs vs. NPCs) are likely to spot each other, this time because the NPCs have lots of chances to get high and low rolls, but not as likely as in the "everyone rolls" scenario.