Series Info...Building Stories, Telling Games #50:

Thinking Mechanically, Part 8: Oddball Resolution Systems

by Travis S. Casey
January 3, 2003

Between "roll vs. threshold" and dice pools (covered in the previous column), a good 90% or more of paper RPG resolution systems are covered; many gamers may never have seen a system which doesn't use one of these two. However, there are other systems. Here's a few which I consider interesting:


The Ironclaw system uses an interesting variation on dice pools. Multiple dice are rolled, and the result is the highest number showing on any of the dice. With just that, the system would be logically equivalent to a dice pool system where only one success is ever needed.

Where Ironclaw differs, however, is in allowing the dice to be of different types. The interesting effect here is that adding a small die to a pool with bigger dice does not increase the maximum performance possible (the highest number that can be rolled), but does make it less likely that a very low number will be rolled — thereby making easy tasks less likely to be failed.

For example, consider a character with a Dexterity rated as 1d12 (for anyone not familiar with RPG dice notation, it's (number of dice)d(size), so that's one twelve-sided die). The character can perform tasks with Dexterity with difficulty as high as 12 — they'll succeed at such a task 1/12 of the time. On the low end, this character can succeed at a Dexterity-related task with a 4 difficulty on 3/4 of their attempts.

Now, let's give the character a tiny bit of training at, say, lock-picking — enough to give them a lockpicking skill with a rating of 1d4. The character's chance of picking a difficulty 12 lock has not changed. We can say that their training doesn't cover locks that tough, so they have to rely on their innate talent. However, against a simple difficulty 4 lock, the character will now only fail if neither die rolls a 4 or better — giving roughly an 82% chance of success, up 7% from what they had before. A bit more training will raise their lock-picking skill to 1d6, at which point they'll succeed against this lock about 88% of the time.

Ironclaw has a "fumble" rule when all 1's are rolled on the dice for a task — if that happens, then something's been messed up badly. Increasing the size of a single dice doesn't decrease the fumble chance by much; going from, say, 1d10 to 1d12 moves fumbles from 10% of the time to about 8%. However, adding extra dice decreases the chance a good deal; a character going from 1d10 to "1d10+1d4" (that's Ironclaw's notation, even though the dice aren't actually being added) has gone from a 10% fumble chance to 2.5%.

Although Ironclaw doesn't make use of it, such a system also can offer a choice for advancement — expanding the limits of one's ability, or increasing the reliability of it on low-difficulty tasks. That is, someone with, say, a 1d8 skill could have the choice of advancing to either 1d10 or to "1d8+1d4". The former allows the character to do things that they couldn't before, while the latter makes the character's skill more reliable on low-difficulty tasks.

It should also be noted that while Ironclaw is somewhat limited by what dice are available, a computerized version of this would have no such limit — if you want to give someone a 1d17 skill, you can.

James Bond 007

Where most RPGs represent difficulty with a threshold, this system took a different tack, representing it with a multiplier to the chance of success. The formula used for the chance of success was:

percent chance of success = (attribute + skill) x ease factor

Attributes and skills both ranged approximately 1 to 15. The "ease factor" for tasks varied from 1/2 to 10. Circumstances which affected the difficulty of a task generally "shifted" the ease factor up or down.

A nice attribute of this system is that difficult tasks are difficult for everyone — in many systems, especially where dice with a small range are used, tasks that are supposed to be extremely difficult are in fact relatively easy to accomplish for a skilled character. The essential problem is that for a standard roll vs. threshold system, the "jumps" in chance of success that a single point added gives are fixed — e.g., in WotC's d20 System, a +1 always increases the chance of success by 5%, no matter how difficult the task is.

With a multiplier, however, the "jumps" vary in size depending on the difficulty of the task — for ease factor 10, each point gives a 10% increase, while for ease factor 1/2, each point gives a .5% increase.

This system was also one of the first ones to make extensive use of success levels — having some successful rolls be better than others. A successful roll was given a "quality rating" (QR) from 1 (best) to 4 (worst). A table was provided to give the QR for different rolls depending on the chance of success, but the underlying principle was that a roll in the "best" 10% of the chance of success was QR1, the next 10% QR2, the next 30% QR3, and all other successful rolls QR4.

Quality ratings were used in such things as deciding how much damage an attack did, whether a persuasion roll is good enough to overcome the target's willpower, and so on. Some uses of the system got quite specific — for example, one module had the characters take part in a golf game, using the QRs of rolls to determine how many strokes a character had to take for a hole.

Dying Earth

The Dying Earth RPG is a recent release, and has a number of interesting ideas. In part 5 of this series, I mentioned its use of descriptors, but another new element it brings is its resolution system.

All resolution in Dying Earth is essentially a coin flip — roll 1d6, and 1-3 is failure, 4-6 success. The specific number rolled indicates the degree of success or failure, with 1 being worst failure and 6 best success.

With an appropriate ability (attribute, skill, whatever), one can get a reroll. The rating of an ability is the number of rerolls that one can get from it before it has to be "refreshed". Each ability has requirements for refreshing it.

One interesting aspect of this is that it puts a decision in the hands of the player. If you don't like what you rolled, you can choose to reroll — but in so doing, you need to consider how many more rerolls you have available for this sort of thing, and how long it's likely to be before you get to refresh them. With this sort of system, players become more likely to simply accept failures at tasks that are relatively unimportant, saving their rerolls for important moments.

The requirements for refreshing abilities are also interesting as a means of enforcing "downtime". Many of them require that the ability in question not be used for several hours or a day of game time.

Don't Look Back: Terror is Never Far Behind

This game's resolution mechanic works like this: positive and negative modifiers to one's action are added together. These modifiers tend to be small, so the final result will generally be in the -5 to +5 range. The player then rolls a number of dice equal to three plus the absolute value of the modifier. If the modifier was positive, the highest three dice are counted; if it was negative, the lowest three dice.

The nice part of this is that the range of results is always the same — 3 to 18. The probability of getting those results changes, but the range does not. Thus, the worst and best results are always possible — they may be very unlikely, but they're still possible. This eliminates any need for special rules for "fumbles" or "criticals".

This system can also easily represent extremely low chances — if, say, a character has a +3 modifier on a roll, the chance of rolling a 3 is about one in 46,000. In most systems, events can't have probabilities that low without requiring extra rolls.

Other Thoughts

Any of these four systems, with appropriate modifications, could be used for an online RPG. But what sorts of systems would work for computerized RPGs that wouldn't work for paper RPGs?

One possibility that I've considered before is a system using consecutive "rolls" to determine the degree of success or failure. It would work like this: the first roll determines simple success or failure. If the first roll is a success, keep rolling until you get a roll that's a failure; the number of successful rolls before failure is the degree of success. If the first roll was a failure, roll until you get a success, and the number of failures is the degree of failure.

In theory one might never stop, so it would probably be wise to set a limit — say, decide that 30 is the highest degree of success or failure you wish to bother with. While 30 consecutive die rolls would take a fair bit of time to do in a paper game, it would hardly take any time at all in a computerized game.

Another thought I've had in the past is a system using ratios. E.g., let's say that character A has a combat score of 15, and character B a score of 17. A's odds of hitting B would be 15:17, and B's odds of hitting A 17:15. In a paper RPG, this would require a fair bit of calculation to deal with, or tables. For a computerized RPG, however, you can simply generate a random number in the range from one to (A's score + B's score), and if it is less than the "active" number, then the attempt is a success. Such a system is conceptually very simple... but due to the restrictions of physical dice, is hard to do without a computer.

What thoughts do you have on systems that could work for a computerized RPG? Speak up! It's what the forums are for!

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