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Edge of Dreams
2012-08-06, 01:45 PM
I'm interested in listing all the different systems of rolling dice to determine outcomes in tabletop RPGs. I want to understand the pros and cons of them, to help me in my own game design endeavors.

I'm going to list the ones I'm familiar with here. Any additions and comments are welcome. I'd love to hear about obscure rolling systems and why you do or don't like them. Non-dice resolution systems would be interesting to hear about as well (aren't there a few games that use a deck of cards?).



Roll Over vs. Roll Under (a.k.a Do I want to roll a high number or a low number?): this is a general principle that just about any dice system can be re-worked to treat either high rolls or low rolls as preferable. Compare old-school THAC0 versus modern D20, for example.
One die: This is the simplest system - roll a single d6, d10, d20, d100, or something else, depending on the game, add your modifiers, and see if you got above the target number. This style is usually pretty quick and easy to handle, and odds of success can be very easy to predict. Larger dice allow more granularity (i.e. a +1 to your roll is a BIG DEAL on a d6, but not really noticeable on a d100)
Sum of Dice: Roll some number of dice (2d6 and 4d6 seem common) and add up the total. The primary difference between this and the one die system is that results form a bell curve - 'average' rolls happen more often, while extremely high or low rolls are a rare event. Fudge dice (as used by the FATE system) are essentially this, rolling 4d3 with values -1, 0, 1 instead of 1, 2, 3. Probability of success is a bit harder to calculate directly, but still somewhat intuitive (at least to me).
X Successes on Y Dice: Roll some number of dice (d10s are common) and see how many of them got above a target number (e.g. 7) - that's how many Successes you got. Harder tasks require more Successes, and better skill or bonuses are usually represented as letting you roll more dice, rather than adding to the number shown. This system has the advantage of requiring less math, but the probability of success feels harder to estimate. Also, this style is good for measuring progress on multi-round tasks - you might need 10 successes but only got 4 this round. That can be treated as progress instead of failure, meaning you only need 6 more successes to finish the task. Finally, there's the disadvantage that this system can lead to rolling LOTS of dice all at the same time, in a way that can be annoying to deal with.


Those are all the generic systems I am familiar with. I know there's a lot of more subtle variations - granularity, relative size of bonuses, how target numbers are determined, etc. - but those details have more to do with the balance of a specific game.

Are there any other dice systems you've encountered? Which do you love, or hate, and why?

Totally Guy
2012-08-06, 05:05 PM
I've found that it's not what dice you roll that really matters. It's why you roll them.

When thinking about how a dice roll works you've got to look at the context surrounding that roll. A resolution mechanic does not work in a vacuum.

What does success mean? What does failure mean? Is there some form of mixed result? Is the GM rolling dice in the open or in secret? Can the player choose not to roll to ask for some other outcome? Do any other game parts move when the dice are rolled? How does the roll relate to advancement? Does the roll influence a pacing mechanic? How are the number of attempts limited? In what way does the player need to act in order to get a bonus to the roll?

Edge of Dreams
2012-08-06, 06:14 PM
I totally agree that there's a lot of context to dice rolls in actual play that I'm ignoring here. I was just trying to focus on the mathematical and practical aspects of how we generate random numbers for our games.

Really, you could take D&D, replace all the d20's with d100's, and multiply everything else by 5, and you'd pretty much have the exact same game (ok, you'd have to do a *little* more math than that...).

Chemiisan
2012-08-06, 07:08 PM
GURPS
Roll Over vs. Roll Under: If it's a skill check, you roll under the target (aim low). Rare situations like Bugs in Gadgeteering actually want to you roll close to the middle, though.
Sum of Dice: 3d6 is the normal roll for a skill check.
X Successes on Y Dice: HT checks for survival and most other cyclic checks follow this pattern.

Eldan
2012-08-06, 07:16 PM
I faintly remember reading of a system where you actually had to roll several dice and get combinations of numbers. I don't remember any details ,but I remember that rolling, say, three of the same number was good, and that there were special number combinations that were especially good.

erikun
2012-08-06, 11:56 PM
Well, the "sum of dice" systems tend to be divided into simple pass/fail resolution and gradient resolutions. A gradient system might have, say, succeeding by 0-4 being a marinal success, but succeeding by 16+ being an overwhelming success. You generally don't see this with a single-die system.

Qin has you roll two d10 dice, with the result being the difference between the two dice. I believe this comes out to the equilivant of 2d10-10, making it functionally the same as a Roll-Under Sum of Dice definition.

IronClaw uses a dicepool, but the size of the dice vary. Rolls are made against another roll, not against a target number. The highest die of each pool are compared together for a single success, the next highest dice are compared, and so on to see which is the victor. The varying dice is unusual, but other systems use the compare-dice method rather than against a target number.

Fudge dice are d6 with the faces +1, +1, 0, 0, -1, -1.

I've heard of other systems that roll dice and then find matching pairs for successes, or play the equilivant of poker with the dice. (both using d6s) And, of course, you have systems that use something other than dice entirely. :smalltongue:

Hylas
2012-08-07, 12:37 AM
One person I know was making a homebrew system (at least I think he came up with it, I didn't ask) which I thought was pretty neat.

You have an attribute which determines the number of dice you roll and your skill which determines what a success is. It's pretty much a "roll under X Successes on Y Dice" system. So nothing new, but an interesting combination.

As for input/comments, I always liked roll under systems better than roll over. Roll over systems generally requires DM judgement to determine if a roll is a success or not. You say "I rolled a 15 on my bluff check" then you wait for the DM to tell you if he feels like having that be a success or not. I once played a system where there was a very general table of "rolling a 1-3 is a failure, 4-8 is an average success, 9-12 is a good success, 13-15 is a huge success, 16+ is legendary" type thing. Now for specific builds you can easily roll a minimum of 5, and easily pass 16 on specific tasks. The game started out with us being okay at stuff, but eventually as we were using specific party members to do specific things eventually the GM started ruling that anything less than a 10 would be a failure because that's where the average roll ended up being. I see this happen with every single roll over system I've played in with a variety of GMs.

With roll under systems you generally have an idea of how well you can do, and can determine success without the need to be a GM. Sure the GM can make things harder or easier by modifying your skill, and he should for different situations, but at least you're aware of this happening and can tell if he's just hosing you at every point.

The same complaint is for X successes on Y dice because the GM can just say "oh, you need more successes than that to do what you want" which was a regular problem I had in Burning Wheel where my poor alchemist constantly needed more successes than dice he could roll to do things. But that was probably because there were no alchemy rules to go with the alchemy skill and the GM didn't feel like making stuff up.

Arbane
2012-08-07, 12:54 AM
The One Roll Engine system rolls a bunch of d10s, and then looks for matches. I haven't played the system, so I don't know the details.

The Legend of the Wulin system is similar: Roll d10s, look for matching sets: The number of matching dice is the tens digit, the number is the 1s digit. So, if you rolled 1,1,4,4,4,5,7, you'd have two sets: 21 and 34.

Geostationary
2012-08-07, 01:09 AM
One that I can think of:

Framewerk [the system name] uses a dice mechanic similar to poker hands, in that you're aiming for straights or multiples of numbers, i.e. 1234 or 4444, that are then added up. The math behind it results in rather odd probability curves. It uses d10s, though there are rules to play with cards instead of dice should you be so inclined.

Khedrac
2012-08-07, 04:54 AM
D% roll below a skill:
Systems vary, I have seen:
lowest roll is best;
highest roll (whilst still under skill) is best (reflects more skilled people usually do better than less skilled when they actually succeed);
doubles (11, 22, 33) best (when under skill) (this was the old Top Secret iirc.);
take the opposing roll off the skill chance to succeed (usually too complex);
take the opposing skill off the chance to succeed (ditto).

Escalating results (usually D% but can be seen on D20). This was the old Rolemaster system:
Roll d% and add skill. If you roll 96-100 (20) roll again and add. Keep going until you don't roll 96-100. If you roll 01-05 (1) roll again and subract, also keep going if you roll 96-100 subtracting again each time.

Then a completely different system - Lost Souls:
Skill results fall into a defined range from appalling attempt to excellent (I cannot remember the names).
NPC's have a straight rating for an ability, e.g. Good defence, Average attack, Appalling climb).
Player's have a numeric ability - they roll D% and consult a chart based on their ability to get a rating.
The result is determined by the different positions in the ranged of ratings:
eg a Good defence v Average attack = no damage.
Good run v Excellent run means they get away.

Knaight
2012-08-07, 05:27 AM
The One Roll Engine system rolls a bunch of d10s, and then looks for matches. I haven't played the system, so I don't know the details.

Expanding this: ORE involves rolling up to 5 d10s for an attribute and up to 5 d10s for a skill, leading to up to 10. Sets of numbers are then found, and the number of the set is called its Height, with the number of dice in the set being the Width. Height determines how well something is done, and there are occasionally Height restrictions, where needing 5+ is extremely difficult. Width determines how quickly something is done. In addition, there are two special d10s - Expert dice and Master dice, with the possibility of having one expert or one master die per roll at most. Expert dice are set to whatever number is desired, at which point the rest of the dice are rolled. Master dice are set to a particular number after the rest of the dice are rolled. Penalties to the size of dice pools remove Expert and Master dice first.

EccentricCircle
2012-08-07, 06:43 AM
I faintly remember reading of a system where you actually had to roll several dice and get combinations of numbers. I don't remember any details ,but I remember that rolling, say, three of the same number was good, and that there were special number combinations that were especially good.

Sounds like One Roll Engine, you roll a pool of ten sided dice, and look for matches. High numbers mean you do better, more matches mean you do it faster. So if I have two 9s in my roll I could use those to do something really thoroughly, or I could go with four fives to do it more sloppily but a lot faster. critical failures occur when you don't get any matches at all.

Knaight
2012-08-07, 07:00 AM
Sounds like One Roll Engine, you roll a pool of ten sided dice, and look for matches. High numbers mean you do better, more matches mean you do it faster. So if I have two 9s in my roll I could use those to do something really thoroughly, or I could go with four fives to do it more sloppily but a lot faster. critical failures occur when you don't get any matches at all.

Essentially, yes. However, critical failure doesn't exist, and failure is more complex than that. There are essentially five ways to fail - somebody acts first, and takes a die out of your set; somebody acts first, making your action impossible; somebody does better and prevents your action from being good enough; you don't get any matches; or you do get matches but they are too low for the specific task. The first two are restricted to conflicts, the last two are for simple tasks with nobody else involved.

Arbane
2012-08-07, 10:55 AM
OH, another one: The newer Warhammer FRPG uses a pool of customized dice, each of which is marked with different possible outcomes: So if you've got only a few dice with success as an possibility. you might add a die to give you a higher chance of success, but which also gives you a chance of exhausting yourself.

TuggyNE
2012-08-07, 07:56 PM
As for input/comments, I always liked roll under systems better than roll over. Roll over systems generally requires DM judgement to determine if a roll is a success or not. You say "I rolled a 15 on my bluff check" then you wait for the DM to tell you if he feels like having that be a success or not. I once played a system where there was a very general table of "rolling a 1-3 is a failure, 4-8 is an average success, 9-12 is a good success, 13-15 is a huge success, 16+ is legendary" type thing. Now for specific builds you can easily roll a minimum of 5, and easily pass 16 on specific tasks. The game started out with us being okay at stuff, but eventually as we were using specific party members to do specific things eventually the GM started ruling that anything less than a 10 would be a failure because that's where the average roll ended up being. I see this happen with every single roll over system I've played in with a variety of GMs.

With roll under systems you generally have an idea of how well you can do, and can determine success without the need to be a GM. Sure the GM can make things harder or easier by modifying your skill, and he should for different situations, but at least you're aware of this happening and can tell if he's just hosing you at every point.

The same complaint is for X successes on Y dice because the GM can just say "oh, you need more successes than that to do what you want" which was a regular problem I had in Burning Wheel where my poor alchemist constantly needed more successes than dice he could roll to do things. But that was probably because there were no alchemy rules to go with the alchemy skill and the GM didn't feel like making stuff up.

Isn't this problem almost entirely a result of either insufficient guidance on target numbers, or GM personality quirks? It doesn't seem like it's related to the actual math at all; the only differences come in how and when to modify target numbers.

kyoryu
2012-08-07, 08:07 PM
The same complaint is for X successes on Y dice because the GM can just say "oh, you need more successes than that to do what you want" which was a regular problem I had in Burning Wheel where my poor alchemist constantly needed more successes than dice he could roll to do things. But that was probably because there were no alchemy rules to go with the alchemy skill and the GM didn't feel like making stuff up.

A) That's no different than having out-of-range DCs.

B) A lot of that is intended in BW. You're supposed to use FoRKs, advantage dice, helping dice, and Artha to get a high enough pool to succeed at more challenging tasks.

prufock
2012-08-07, 10:14 PM
Not a separate system (still falls under "one die"), but you can have degrees of success or failure in relation to a target DC. See Mutants and Masterminds 3e as an example. Each 5 points over/under the DC is a degree of success/failure.

celtois
2012-08-08, 02:51 AM
Game of Thrones by Green Ronin uses a #D6 + #BonusD6. Which basically functions as roll all the dice, and drop a number of dice equal to the number of bonus dice you rolled.

I really like it.

Knaight
2012-08-08, 03:41 AM
There are roll and keep systems in a whole bunch of games, where you roll a bunch of dice, and keep a certain number of the best (or occasionally worst).

Zaggab
2012-08-08, 05:55 AM
In Savage Worlds, Wildcards (PC's and important NPC's) get a "wild die" with each roll, a d6.

And how good you are at a skill is determined by the size of the dice you use, going from 1d4 to 1d12.

So, a PC with d4 in a skill rolls 1d4 and 1d6, and picks the highest die to determine success (thus a roll high system). Plus, the dice can "ace", so if you roll the maximum number, you get to roll again and add the the new roll to the old one. Which makes d4 a fun die, since it aces so easily.

This leads to very wonky probability curves, like when a hero rolls 1d4 and 1d6, by acing the wild die several times in a row, ends up with a Fighting roll of 29. Happened during one of my games. Though he still only rolled 5 for damage (not enough to even affect the target).

Oh, and the acing works for damage roll as well. You might think that someone rolling 2d6 for damage would have a fairly predictable damage output, but every time a 6 is rolled opens up for really high damage rolls. Highest I've seen was 34.

Stubbazubba
2012-08-08, 11:08 AM
The Mistborn Adventure Game has you roll a pool of d6's and look for your highest pair, 1-5, and every 6 bumps it up one higher.

Marvel Heroic Roleplaying has you roll a pool of various-sized dice, and pick the top 2 (for accuracy) and the next 1 (for effect), generally. So it's a roll-and-keep system.

The One Ring uses 1d12 + Xd6, where X can be 0-6, sum of dice. That gets annoying really fast (it takes me 4-5 seconds to sum up 4 or more numbers, and that's kind of noticeable in the middle of a combat), but it gives you great mechanics; a nat 1 on the d12 is an automatic failure, a nat 12 is an automatic success, while nat 6's on the d6 give you higher degrees of success. That many different ways of success that are that obvious just isn't possible in a one die system.

I personally prefer dicepool systems (roll XdY, look for Successes); rolling a pile of dice and going through and counting successes is just intrinsically fun for me, way more so than doing math, even if the math is trivially simple like d20 + modifiers. I can and have literally spent hours of time (not all in one sitting, but in total) just rolling 12 d6's and counting out hits, just for the heck of it. I certainly don't do that with any other system.