Opposed to Proposed Opposed

There's a fairly common house-rule for "Opposed Checks" in Warhammer FRP 3rd that I decided long ago not to use in my campaign. It keeps coming up, because the official rule for opposed checks in the game is a little clunky and rewards whichever party acts first. (My Stealth vs your Observation is usually a better die pool for me than your Observation vs my Stealth would be.)

The proposed opposed check house-rule is:

valvorik, on 13 May 2014 - 04:43 AM, said:A variant opposed check rule floating around has been to use "challenge dice equal to opposing stat -2", so sneaking past Int 6 is 4 challenge dice.

So if your character's Intelligence is 3, all Stealth checks against them would be vs 1 Purple die. If your Int is 2 or less, there's no purple dice on those rolls. 

(What follows is a slightly revised version of something I posted at FFG's Warhammer FRP forums. I'm cross-posting it here largely to preserve the math that went into it.)

I know a lot of GMs use that as a house-rule, but I don’t feel it improves the odds (or game experience) in most situations. The only thing I particularly like about that rule is that it’s simple and requires no chart-referencing or division at the table top.  That alone is almost enough for me to adopt it, but in the end I decided against it after running the math on how it affects the odds of common rolls.

(As a reminder: PCs can have stats from 2 to 6, but no higher than 5 at character creation. NPCs can have stats below or above that range, but it's somewhat rare. That's why my table starts with 2 and ends with 6, but has opposed values of 1 to 7.)

Opposed Stats    | original success rate    | house-rule success rate

2 opposed by 1     44%             75%
2 opposed by 2     25%             75%
2 opposed by 3     14%             44%
2 opposed by 4      8%              25%
2 opposed by 5      8%              14%
2 opposed by 6      8%               8%
2 opposed by 7      8%               4%

3 opposed by 1     88%             88%
3 opposed by 2     59%             88%
3 opposed by 3     38%             59%
3 opposed by 4     24%             38%
3 opposed by 5     24%             24%
3 opposed by 6     14%             14%
3 opposed by 7     14%              9%

4 opposed by 1     94%             94%
4 opposed by 2     72%             94%
4 opposed by 3     72%             72%
4 opposed by 4     51%             51%
4 opposed by 5     37%             37%
4 opposed by 6     37%             23%
4 opposed by 7     37%             14%

5 opposed by 1     97%             97%
5 opposed by 2     97%             97%
5 opposed by 3     81%             81%
5 opposed by 4     81%             63%
5 opposed by 5     63%             46%
5 opposed by 6     46%             32%
5 opposed by 7     46%             21%

6 opposed by 1     98%             98%
6 opposed by 2     98%             98%
6 opposed by 3     88%             88%
6 opposed by 4     88%             72%
6 opposed by 5     88%             56%
6 opposed by 6     72%             42%
6 opposed by 7     56%             30%

Which stats benefit from this house-rule?  I find I don't like the answers to that question.

A “2” in something is now much better at offense, and only weaker at defense when being targeted by someone with a low-to-middling stat. I think that’s overall an improvement for anyone with a “2”, especially PCs. This is because it’s rare that an NPC will target you with an opposed check using a stat that the NPC has a 3 or lower in. Sure, a soldier or goblin will often attack you with Str 3, but that will be vs Target Defense, not vs your dump stat. A hypothetical min-maxed PC with a Fellowship of 2 has a 44% chance of talking his way past the city-watch using this house-rule, where the original rules would have that success rate down at a punishing 14%. PCs with a 2 in Agi, Int or Fel will hardly every suffer for it, and this makes that even more true. So I kinda prefer the original rules, just because they’re harder on munchkins.

Average PCs, making fairly typical checks, won’t see much of a difference. They’ll be a little better at affecting people far below them in stats, and a little worse at affecting those who greatly outclass them. Neither is going to happen often enough to make a big impact. 3 vs 3 gets easier, and that's the only mid-range roll with a major change that's likely to come up often at all. In my experience, PCs with a 3 in a stat are pretty reluctant to use it (even if it's not an opposed check), and there's almost always someone else in the party who can fill that niche better. I see neither gain nor loss from this house-rule for this segment of characters.

At the other end of the spectrum, high stats (5 or above) become much less effective against other high-stat characters when using this house-rule. If you’ve got a 5 in something, your active/aggressive use of that stat suffers, but oddly enough your passive/defensive (opposing) use of that stat gets a big bump. That might actually work really well if you’re using ever “player-facing” mechanic you can, as it avoids the problem built-in to WFRP3 where if the players make all the rolls their success rates are much higher than if the GM grabs the dice more often. It's also a benefit if your scenario is relying on a lot of mystery plots, as it protects your Black Cowls and Moriartys a bit from players just spam-Intuition-ing every NPC. Henchmen and average-or-below flunkies will still get broken or revealed by Str 5 Intimidate or Int 5 Intuition checks, but at least the Big Bad can stand in the same room as the PCs without being immediately outed by the wizard/scholar/verenean in the party. The chance of scoring a chaos star while making those Int checks is greatly increased, which helps make spamming them much less attractive.

That last bit is a strong benefit to the game, but it comes at the cost of downgrading many of the best Social Actions and non-combat spells when used against above-average targets. “Influence the Target” takes a nose-dive under this rule, at least when the target is a nobleman with a high Fellowship (who, I should mention, already gets numerous social-encounter benefits for being a nobleman such as increased Shame soak, bonus boon-lines, and minimum Social initiative). The lower success rate further pushes the GM towards ignoring the rules for Shame Thresholds and Progress Trackers in favor of single-roll social encounters just to keep the plot moving (a pressure that GMs feel already with the core system and the overly-long trackers in some of the published expansions). While the total change isn't game-breaking, I really don't like that it only penalizes characters whose focus is outside of combat.

TL;DR: The common House-rule (opposed checks use Purple = opposed stat -2) is a good match for Mystery plots with competent villains, and is better the more you have PCs roll instead of NPCs. The downside is that it rewards min-maxed and combat-focused characters, and devalues Social actions.