Monday, July 19, 2010

Universal Mechanic

You can use this in almost any game. It's for when the task resolution system native to that game sucks or is confusing or doesn't cover a given situation. It's derived--in my mind--from the Warhammer 40k melee combat system but probably exists in other games, too. In fact, I'll be kinda shocked if I invented this. Anyway...

Rolling to do something the other person doesn't want you to do (grabbing something away from him/her or psionically zapping them, for example), or something otherwise competitive (picking up an object first) or even (if you wanna go crazy with it) an action against a static thing (trying to read a difficult book) is an opposed roll.

The die roll's based on the relevant stat. If, say, you're car-chasing someone, that'd be dex or agility or drive skill vs, the opponent's dex, agility or drive skill. If you're trying to hit a pedestrian that could be drive skill vs. dodge skill. If you're trying to charm a sentry that could be your charisma vs. the sentry's wisdom. With reading a book it could be the intelligence of the reader vs. the difficulty of the book (measured on a scale of 3-18 if it was D&D, just like intelligence.) As long as the two stats being paired are measured on the same scale (or can be mentally converted to the same scale), you're cool. If you have "fix computers" at 34% then the GM could say "Ok, on a scale of 1-100 how hard is this computer to fix?" and pick a number.

Contestants both roll dice. The die rolled should be whatever die's value is nearest to the higher contestants stat rounded up to the nearest die (i.e. if the higher stat's a 5, roll d6, if it's 70, roll d100, etc.)

Anyway, both sides roll a die and add their stat. High roll wins.

Example: Teddy and Cheswick are stalking each other through the jungles of Marsoopia. Who sees who first? Teddy's wisdom is 8, Cheswick's is 12. They both roll a d12 to see which one notices the subtle signs of their quarry first. Teddy rolls a 7, Cheswick rolls a 2. Teddy's at 7 + 8 =15, Cheswick's at 12 + 2 = 14. Teddy sees Cheswick first.

(Note: in a game where the ability scores represent vastly differing power levels--like a super-hero game--roll a die that equal to half the spread of the stat. i.e. If it's a 3-18 system and an 18 represents Thorlike strength, contestants roll a d10 instead of a d20. In Warhammer it's a 1-10 system with 10 representing greater demons and they use a d6. The idea being that the chances of the Hulk getting out arm-wrestled by Jimmy Olsen decrease if you use a smaller die.)

I notice this is considerably more fun than just having one person roll, and avoids having to decide which character is "active" and which is "passive" and crap like that. Who's active and who's passive when the medusa's trying to look at you while you're trying to get her to look at a mirror?


Notes on using this for combat:

Since most systems either have--like D&D--one roll that represents getting past both the target's nimbleness and armor combined or else have dodging cost an action for the dodger, you wouldn't normally want to use this for most combat since it'd throw off the whole system. It works real well for grappling, however.


Obviously there are some pain-in-ass exceptions here that make this mechanic harder to use in certain games: halving a % system means using a d50 which is kinda hard to come by, and sometimes you will end up with a stat vs. a stat on a different number scale. However, certain kinds of minds will be able to use a little creative multiplication and division to get past this stuff. Certain other kinds of minds will say how they're perfectly happy with all aspects of the system they're using so fuck off, which is fine, too.


nextautumn said...

I've been doing something similar to this for a while, except I figure the difference between the two contestants scores and give that number as a bonus to the better contestants roll. So, in your example, instead of adding 8 to Teddy's roll and 12 to Cheswick's, I'd only add 4 to Cheswick's.

Nope said...

The miniature game Infinity does this mechanic(well a similar one).

Each character rolls against their stat(not a modifier but a score), and if the result is equal to or lower it is a success.

But, whichever character naturally rolls a number higher than the other character is the victor. There may have been modifiers involved at this point, or it may have been built in to the score, it's been awhile.

As a twist if one character rolls the exact number of their score, it was a critical I think. The game is from Spain, I think it's still being played and has quickstart rules.

Kevin Mac said...

I try to avoid task roll vs. task roll because it starts to come off a bit like Hero System or something similar, and I try to keep it simple ol' D&D rather than an extension of my Champions games. Just stat or less on D20.

Zak Sabbath said...

in practice, that's actually how I do it, but I wrote it this way 'cause I thought it'd be easier to read.

sure, but then what do you do when tasks are contested? how would you judge an arm-wrestling contes?

Anonymous said...

For an opposed stat roll, how about both roll d20, and the one who rolls higher but still under his stat wins. if they roll the same, the one with the higher stat wins, and if neither rolls under their stat, its a tie/stalemate.

Taellosse said...

GURPS uses opposed rolls extensively. Of course, they use 3d6 for everything (except damage--that can be more or fewer dice), so there's no figuring out what kind of dice to use. But anytime there's 2 forces acting in opposition--even combat--opposed rolls happen. I'm rather fond of it, for exactly the reasons you mention--it allows for more dynamism, since static target numbers are far less common.

Zak Sabbath said...

because in most cases I think the stalemate isn't really a fun or productive result.

however, i could be persuaded otherwise.

sounds good to me. GURPS has the lowest charisma score of any game system, but that probably shouldn;t put a grown-up off it.

Anonymous said...

Zak, if you don't like stalemates, just replace that with "if both roll over their stat, the one who rolled higher wins".

Anonymous said...

Another, much simpler (and a lot more random) take on opposed rolls is the one used by Lord of the Rings Strategy Battle Game: Both roll a die. Higher wins. On a tie, whoever has the higher stat wins.

Zak Sabbath said...

seems like the "if both roll over..." etc. just makes it almost exactly the same, only slightly more complicated (2 rules instead of one) and slightly less ability-based. (i.e. if they both have a low stat, it's suddenly more random. In my method the stat always matters.)

Zzarchov said...

In Piecemeal I use opposed rolls consistently (the big one being combat and stealth). Its always a d20 + mod VS d20 + mod though.

So d20 + attack bonus vs d20 + defense bonus for combat.

Someone hiding would roll their d20 + mod versus the spotter (d20 + mod). The modifier is usually the entirity of a stat + a bonus. So someone hiding might be a d20 + 12 int + 3 bonus vs d20 + 8 + 2 etc.

Opposed rolls are nice in that they give someone something to do when its not their turn.

Anonymous said...

Well, every method has its pros and cons. A rather simple opposed roll system is the one in Lord of the Rings Strategy Battle game, where both sides roll a d6, higher wins. On a tie, whoever has the higher stat wins. This means whoever is better wins about 67% of the time, but it doesn't really matter how much the better one is better.

Or you could roll d6 plus stat modifier, which makes for slightly simpler math ((1-6) + (1-3)) than die plus stat ((1-20) + (1-18)).

Zak Sabbath said...

that works in D&D but not in any game. Some games don;t have derived stats

Zak Sabbath said...

(i'm re-posting this underneath here for clarity's sake)

navdi said...

What it boils down to is all you need to do is determine ratio of chance to stat. If your chance range (the die's range) is larger than your stat range, chance plays a bigger part and even the puniest guy in the world has a chance to squirm out of the grasp of Demogorgon. On the other hand, if the stat range is larger, the stat matters more than chance.

And this is me stating the obvious. ;)

Zak Sabbath said...

do you find that advancement begins to matter less,since the whole system is more random?

squidman said...

This is a very elegant system. I like it a lot!

Mincer of Logic said...

This is very similar to opposed rolls in the AGE system (created by Green Ronin for the Dragon Age licensed game system).

All their die rolls are 3d6 + stat, so the two players each roll for their appropriate stat, add 2 if they have the approriate Focus. GM can apply situational modifiers to either roll (for instance, higher ground).

Zzarchov said...

@Zak S

I wouldn't say that advancement matters less, but there is definately a greater range of possibilities. The breakdown works much the same, ie) instead of a THAC0 18 attack roll against AC8, its a d20 + 2 vs d20 +2 for instance.

so still 50% chance of hitting either way but now there is the chance for an 18 on the attack and a 2 on the defence for some extreme difference between attack and defence.

Zak Sabbath said...


I'm just wondering if the PCs decide they're definitively outclassed less often, since they always have a chance of hitting somebody. Or if, in general, relative strength of the 2 sides is less important, leading to less strategic play.

Zzarchov said...

@Zak S

oh there is definately more of a thought of "I have a chance" at points, thinking "C'mon..I just need an 18+ while he rolls a 5 or less.."

BUT, that works about in equal measures the reverse: Not wanting to pick a pointless fight because hey "They could roll a 19 to your 3 and mess you up."

I think this would be a bigger problem if people we not used to natural 20's being auto-success (or natural 1 being a failure). The chance of "Rolling that 20" tends to be the biggest draw above the option to roll "34 above the target"

frijoles junior said...

I've been working toward a system much like Zzarchov's, in search of a single-opposed roll as a quicker method of combat resolution - to avoid the problem of whiff-fests where nothing happens round after round. IMHO, every round should result in some change of state in a conflict.

But since I've been loathe to part with my beloved d20 because it has the coolest shape, I've had my concerns about "swinginess" of combat, since opposed d20s can have up to a 39 point spread. Your simple solution of dropping the die type cuts the knotty problem neatly, so thank you for that.

I'm not sure that I can embrace a system based around boring old cubes, though. Hmmm. d12s are almost as cool as d20s, but your unassailable logic is pointing me toward something smaller. d8-based universal action resolution system, here I come!

The Cramp said...

It was pointed out to me that in 3rd Edition D&D AC basically just has the defender "Take 10." sometimes I will flip this and have attacks be Attack + 10, and roll the defenders AC. In particular when the PC's brutally outclass who ever they are attacking. I roll in the open and get to say, "18, the poor bastard gets out of the way!" and they sort of get the point they are being bullies/tyrants/murderers.

A GM said...


Maybe there's a narrative solution for the dice woes when a stalemate occurs --
Whatever the GM decides is interesting, dramatic or fun, happens on a stalemate.
Anything from the two glaring at each other from behind clashed weapons, to stepping in a previous someone's entrails, both combatant discover the ground is riddled with sinkholes as they both suddenly drop into a couple seperate ones. It gives the GM a chance to interject something into a null result and keep things interesting.

ravenconspiracy said...

*Pushes back nerdy glasses which catch the light with a sudden keening gleam*

I assume you were basing this off of the (now outdated) 2nd edition WH40K close combat rules?

*snort* Those were the days...

ravenconspiracy said...

Oh... almost forgot.

Would you include anything like the rules for multiple participants, extra dice (attacks), fumbles, and criticals?

Zak Sabbath said...

i don't see why you should bother when you can just create a mechanic that skips stalemate altogether with no downside at all.

Gm narration is all fine and good, but part of the fun is when everyone knows it all hangs on chance and you get to watch chance do its thing.

Zak Sabbath said...


of course not--it's based on 1st edition wh40k .

as for fumbles, crits, and multiple participants--of course. that's cake, don;t even need to change the existing d&D rules. Extra dice is more ocmplicated--depends on the game.

Blauwe Bart said...

I like the idea of using smaller dice for contested rolls a lot. IMO a D10 works fine in D&D3, especially for such small stats like Initiative or the first 7 levels of the PCs.
D20 just leaves too much to chance for my taste. Players also feel like they get cheated out of their skillpoints because spending a whole level of them on one skill still means little difference on a D20.
I think it supports getting minor skills as well, instead of focusing unnaturally.

For outclassing: Vampire-The Masquerade has a nice optional rule, meant mostly for PCs. In Vampire you roll a D10 for each relevant statpoint you have against a DC of 6 by default.
With the optional rule, You automatically succeed on any test in which the number of D10 you may roll are more than the difficulty.

Bit like "Take 10" but more elegant.

Menace 3 Society said...

I suppose you're aware of CoC/BRP's Resistance Table, which accomplishes much the same thing (to compare skill vs. stat you just divide the skill by 5).

ravenconspiracy said...

@ Zak

1st edition 40k (AKA Rogue Trader) used a target number generated by comparing Weapon Skills, in the same manner as Warhammer Fantasy Battles and 3rd edition and later 40k did. Attack rolls were rolled on each side in initiative order just like Fantasy and later editions.

Only 2E 40k and Necromunda (and maybe GorkaMorka also?) use the heads-up rolling method you are talking about.

Zak Sabbath said...


then i suppose our group just house-ruled over top of that chart a few years before GW decided to do it themselves.

ravenconspiracy said...



The close combat in Rogue Trader is definately not like you're describing so if you really were using "2e Combat" prior to release...

My only theory would be that variant close combat rules were introduced via White Dwarf or one of the old Compendiums which was adopted as the official version for 2nd ed when it was released later.

YoungWilliam said...

If you had some sort of mutant malleable dice that could easily have any number of sides, I presume it'd just go with "higher stat" instead of any rounding up?

Zak Sabbath said...