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Storyteller» Forums » Rules

Subject: Storyteller System flaws rss

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I would like to document some interesting flaws in the core action resolution mechanic in the Storyteller system. If you are familiar with this system, you can skip the introductory background that explains how it works.


Background

Characters have a number of Attributes and Abilities each of which is rated from 0 to 5. 2 is an average human score. 5 is the highest human potential. Some supernatural powers may raise the values beyond this maximum.

An action is typically tested by the appropriate combination of attribute and ability, adding the values together to calculate the size of the dice pool. This many ten-sided dice (with values read as 1 to 10) are rolled against a target difficulty. Each individual die rolling equal to or higher than the difficulty counts as a success. Each individual die rolling a 1 deducts one of these successes. Rolling more 1s than successes is called a botch; rolling a net total of 0 successes is a failure; a positive amount of successes is a success, with the number of net successes determining the degree of success (typically on a scale of 1 to 5).

Note that when the Storyteller system was revised in 1998, the definition of a botch changed subtly: a botch would only result if there was at least one 1 rolled, and no successes at all (as opposed to a greater number of 1s than successes).

So usually dice pool sizes range from one to ten dice. Even with supernatural powers, it is unusual that more than twenty dice are rolled.

A standard target difficulty number is 6, although the difficulty can range from 2 to 10.


Flaw: Difficulty 2

Any individual die roll can only be a success (+1) or a botch (-1). This means that when rolling an odd number of dice, it is impossible to fail; only to succeed or botch. But when rolling an even number of dice, one can succeed, fail, or botch.

This skews the probability distribution in odd ways:


Flaw: Probability of Botching
Affected core rules:
Vampire: The Masquerade (1st Edition) (1991)
Werewolf: The Apocalypse (1st Edition) (1991)
Mage: The Ascension (1st Edition) (1993)
Wraith: The Oblivion (1st Edition) (1994)
Changeling: The Dreaming (1st Edition) (1995)
Vampire: The Masquerade (2nd Edition) (1992)
Werewolf: The Apocalypse (2nd Edition) (1994)
Mage: The Ascension (2nd Edition) (1995)
Wraith: The Oblivion (2nd Edition) (1996)
Changeling: The Dreaming (2nd Edition) (1997)
Vampire: The Dark Ages (1996)
Werewolf: The Wild West (1997)
Mage: The Sorcerers Crusade (1998)
Note that this flaw was fixed in the system starting
with the revised edition of Vampire: The Masquerade,
and the following core rules are all unaffected:

Vampire: The Masquerade (Revised Edition) (1998)
Werewolf: The Apocalypse (2nd Edition) (2000)
Mage: The Ascension (Revised Edition) (2000)
Dark Ages: Vampire (2002)
Dark Ages Basic Rules (2004)
Hunter: The Reckoning (1999)
Demon: The Fallen (2002)
Orpheus (2003)
Vampire: The Masquerade (20th Anniversary Edition) (2011)
Werewolf: The Apocalypse (20th Anniversary Edition) (2012)
It would be a reasonable assumption to make that as a character improves in their ability to perform a particular task, that the chance of a critical failure (botch) should decrease; or at least should not increase. However this is not always the case with the system as written: for a fixed target difficulty, the probability of botching can sometimes increase as your dice pool increases.

The specific ranges where this flaw occurs are...

Difficulty 2: the probability of botching when rolling an odd number of dice is higher than when rolling one less die.

Difficulty 2: the probability of botching when rolling 3 dice is higher than when rolling 2 dice.

Difficulty 7: the probability of botching when rolling 2 or 3 dice is higher than when rolling 1 die.

Difficulty 8: the probability of botching when rolling 2 to 8 dice is higher than when rolling 1 die; the probability of botching when rolling 3 to 4 dice is higher than when rolling 2 dice.

Difficulty 9: the probability of botching when rolling 2 to 36 dice is higher than when rolling 1 die; the probability of botching when rolling 3 to 19 dice is higher than when rolling 2 dice; the probability of botching when rolling 4 to 12 dice is higher than when rolling 3 dice; the probability of botching when rolling 5 to 9 dice is higher than when rolling 4 dice; the probability of botching when rolling 6 to 7 dice is higher than when rolling 5 dice.

Difficulty 10: the probability of botching always increases, the more dice that you roll.

As mentioned above, the revised edition of the rules starting from 1998 fixed this bug. Instead, botches could only be rolled if there was at least one 1 rolled, and no successes at all (as opposed to a greater number of 1s than successes). This gave a maximum probability of botching of 10% for a dice pool of 1, with a reduced probability of botching as the dice pool increased. Probabilities of success were completely unaffected.

This was a fine solution, and completely fixed the problem (after only seven years of product sales).



Probability Distributions

Here are graphs for all difficulties; open them up for a larger view. The probabilities are also listed in a comment to each image, to 0.1%.
Difficulty 2:

Difficulty 5:

Difficulty 8:
Difficulty 3:

Difficulty 6:

Difficulty 9:
Difficulty 4:

Difficulty 7:

Difficulty 10:

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Hans Messersmith
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Nice article Stelio.

Here is another article covering similar territory...

http://www.scribd.com/doc/46230301/d10-Probability

It is of interest mostly because of the formulas it derives.
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Strange that some game designers don't do the maths as a matter of course. Not everyone's a mathematician, but hopefully there's a friend of a friend or an excel template or something to help with probability.
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In addition to the revised Vampire probabilities (when you get around to them), I'd also be interested in a comparison to nWoD.
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He went overloading on testing and coding and his name was
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dysjunct wrote:
In addition to the revised Vampire probabilities (when you get around to them), I'd also be interested in a comparison to nWoD.

Article, graphs, and tabulated probabilities all updated to reflect the improvements introduced by the revised edition of the rules.

So... what are the full details of the nWoD mechanics?
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I'm no expert, I've only played nWoD once, and I'm in my cups, but I think it is:

- basically the same, dots etc.
- however target numbers are fixed. 8+ is always a success, 10s count as successes and get rerolled, with exploding possible.
- number of successes is always degree of success, using the standard 1=marginal, 3=complete, etc.
- situational difficulty substracts dice from the pool.
- botching is only possible if lack of skill and/or difficulty reduces your pool to one die or fewer. In that case, you still get to roll a die, but a one is a botch.

Please correct, nWoD fans!
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Samuel Sol
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This sounds a lot like Scion and Exalted, so I think it is correct for nWoD
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Blue Tyson
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That always annoyed me, too. I never played the new version, though.
 
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