Opposed rolls

[Triff]

Time this topic got its own thread!

Roll low, roll high, etc. Go on!

I prefer to roll low always, which is why I prefer the RQ:AiG method.

SGL.

[fmitchell]

First imagine a character with a 90% skill vs. a character with 30% skill. Basic probabilities are as follows, ignoring criticals and fumbles:

Ninety wins, Thirty loses => 0.90 * 0.70 = 0.63 or 63%
Ninety loses, Thirty wins => 0.10 * 0.30 = 0.03 or 03%
Ninety loses, Thirty loses => 0.10 * 0.70 = 0.06 or 07%
Ninety wins, Thirty wins => 0.90 * 0.30 = 0.27 or 27%

So the question is really about the last case, which is either second-most probable or most probable (e.g. if both characters's skills are above 50%)

BTW, "Roll high but not over" is mathematically equivalent to "Roll under for the largest difference", and requires one less subtraction.

I'll crunch some numbers for percentiles, but in the meantime take a look at my HeroQuest probability table. HeroQuest uses opposed d20 rules, with 1 a Critical and 20 a Fumble; if both characters succeed or fail, the one with the lower absolute roll loses. The "Marginal Victory" and "Marginal Defeat" columns represent the last case; the 18 vs. 6 row is roughly equivalent to 90% vs. 30%.

[frogspawner]

(Regarding opposition to opposed rolls: )

Originally Posted by Lord Twig

I can understand the "keep it moving" mentality, but there is a problem with roll and move on. If a PC makes a stealth roll and sneaks past the guard, no problem. But if an NPC assassin makes a stealth roll and sneaks past the PC they are going to wonder why they didn't get a chance to see the person. Particularly if it results in the death of a PC.

"But I have a Spot of 100%! How could he sneak past me?"

If you only roll the Sneak, a character with 100%+ will almost never (96-100) be spotted no matter how good a lookout you are.

Originally Posted by badcat

You modify the assassin's stealth roll. And/or allow a modified listen roll for the prospective victim. Or do a POW:POW roll or other resistance table roll. Or treat it as an ambush (it's not necessarily going to be fatal, even if the assassin hits...this ain't D&D). Lots of ways or combinations of ways, and they all work without bogging things down with a counter-intuitive resisted roll, and they create tension and fun just the same. Hey, whatever works.

Originally Posted by Trifletraxor

I liked the RQ:AiG version. A successful sneak/hide halved the listen/scan chance of the guard (more if the guard was not expecting anything).

I'd prefer to keep the (Sneak/Spot) rolls entirely separate, and not affect each other at all if possible. Something more like the attack v parry system in combat, perhaps? (without opposed rolls, of course!)

Or maybe somehow use a concept of "layers" of success: Just sneaking by/away is easy (one success required); but sneaking close to someone to pick pockets is harder (two successes); and assasination is even harder (a third success required)?

Currently I use a system where each side makes it's rolls (Sneak/Hide and Listen/Spot respectively) but the success levels just contribute bonus/penalties to a final perception-type Idea Roll by the spotter. Still not really happy with this method though.

[frogspawner]

I think the "Hide/Spot duel" is the classic example that makes people perceive a need for opposed rolls. So if we can come up with a good system for it, using a sequence of normal rolls, then we can forget the whole Opposed Rolls issue... and the hard maths!

[NickMiddleton]

Originally Posted by frogspawner

I think the "Hide/Spot duel" is the classic example that makes people perceive a need for opposed rolls. So if we can come up with a good system for it, using a sequence of normal rolls, then we can forget the whole Opposed Rolls issue... and the hard maths!

The "hard maths" bit baffles me:

Better level of success wins (but losers success ameliorates the winners success a bit).

If success levels are equal, best roll wins (I use margin i.e. target-roll, as a personal preference, but higher roll is equivalent).

The only "quirk" (assuming that the amelioration ONLY occurs after determining who wins) is that on a tie of normal successes, the win is cancelled by the losers right to down grade the winners success by one level from normal success to normal failure; but that's basically what happens with a normal successful attack vs a normal successful parry anyway. One could then rule in that case that the winner achieved a "partial success".

As I say, when success levels are tied I use "best margin" (i.e. target - roll) as it feels more easthetically appropriate to the main BRP paradigm of rolling low on d100 is always better, and frankly it's usually obvious without maths who has the margin, so the subtraction is rarely necessary. But, as pointed out, "roll under, but as high as possibly" is mathematically equivalent, so I really don't see what the fuss about the opposed roll mechanic is - it's simple, straighforward and doesn't involve any significant maths.

Plus there were three optional variants in the playtest draft IIRC...

Cheers,

Nick Middleton

[deleriad]

I have been using opposed rolls in BRP games ever since I read Pendragon and a light clicked on. Not seen the new BRP rules but my house campaigns collapsed specials and criticals into one (as MRQ does) which meant that I was happier with the range of outcomes. I'm in the camp which tries to read the result off the dice without calculation so I use highest roll wins if the result is a tie. I've never come across any resistance to this among players.

"Made by most" is more aesthetically pleasing but when I tried it (it was the first way I tried to run ORs because it's the most obvious way) there were just enough "hang-ons" that they seemed to interfere with the game and once someone pointed out that I could do highest wins then that ran much more smoothly with my play style. I did occasionally find that having criticals, specials and normals felt congested once opposed rolls started to get used a lot, which is why I collapsed criticals and specials together.

I'm also becoming increasingly converted to opposed rolls in combat. I don't use MRQ's method because it's a mess but with critical/normal/partial results it runs smoothly and all you have to do is look at your dice. It feels about the same level of complexity as RQ3.

Personally I like the deep logic behind opposed rolls. You make a skill test when it's just you against a passive resistance and a skill contest when it's you against someone else. In a skill test there is a fixed modifier affecting your result. In a skill contest there's a variable modifier affecting your result.

[soltakss]

There's no Hard Maths involved. Believe me, I've done some hard maths (although not too hard) and this isn't it.

A critical success beats a special, normal, failure or fumble.
A special success beats a normal, failure or fumble.
A normal success beats a failure of fumble.
A failure beats a fumble.

Simple, assuming you can work out whether you've succeeded/failed/fumbled/specialed/criticaled.

If you get the same result (i.e. both Fumble, both Fail, both succeed normally, both special or both critical) then you have to work out who has done better.

I prefer "succeeded by most", other people prefer "highest roll", they are the same. Normally it doesn't take much calculation to work out "succeeded by most" and no calculation to work out "highest roll".

So, where's the problem?

I'm not sure about the loser's level of success having an effect on the victor's levelm of success as I don't have BRP yet. presumably that is to differentiate a critical vs special from a critical vs failure, for example. It's pretty irrelevant if that's the case as BRP doesn't have any meaningful rules for effects based on differences between levels of success.

[soltakss]

By the way, is BRP still using 1/5th Special, 1/20th Critical? What about Fumbles? Are they still 1/20th of the failure chance?

I feel it's time for some concrete examples of skill vs skill rather than wishy-washy probabilities.

[frogspawner]

Originally Posted by NickMiddleton

As I say, when success levels are tied I use "best margin" (i.e. target - roll) ...

There you go - one number minus another! Hard maths!

[NickMiddleton]

Originally Posted by soltakss

...I'm not sure about the loser's level of success having an effect on the victor's levelm of success as I don't have BRP yet. Presumably that is to differentiate a critical vs special from a critical vs failure, for example. It's pretty irrelevant if that's the case as BRP doesn't have any meaningful rules for effects based on differences between levels of success.

Precisely the point is that the new BRP DOES have "...meaningful rules for effects based on differences between levels of success..." for every skill. The new BRP opposed skill rule is basically the fairly well known fix used by a lot of RQIII fans for the percieved weakness of Dodging (i.e. that a normal successful Dodge was bugger all use againsts a special or critical hit, unlike a normal Parry which had some effectiveness...)

Originally Posted by soltakss

By the way, is BRP still using 1/5th Special, 1/20th Critical? What about Fumbles? Are they still 1/20th of the failure chance?

Certainly was in the playtest draft and from what I've seen / read about edition zero that's still the case. Arguably, the default should perhaps have been the Stormbringer first edition scheme (Fumble / Failure / Success / Critical on 10% thresholds), but AFAIK it's the RQIII scheme that's assumed throughout.

Originally Posted by frogspwaner

There you go - one number minus another! Hard maths!

Are you really suggesting that given a two rolls against two percentile targets you find it that hard to give an order of magnitude approximation?

"I only made my sneak by twenty odd" "That's too bad, the guard is very alert - he made the spot by about forty odd so he's spotted you". In very few cases will the exact margin be relevant. And, as has been said repeatedly, "highest roll wins on same success level" is mathematically equivalent to the subtraction, so the rule as written DOESN'T require even the terrifying complexities of basic two digit integer subtraction...

Nick Middleton