System Blending and Probability Mapping

webtech's picture

I devised a conversion table for mapping *W stats to 1d100 (for systems that use percentile skill scores, etc). That post is below. But rather than focus on this one particular mapping, I have decided to open up a conversation on ALL sorts of probability maps or stat conversions that can be used to hybridize two game systems.

Are you a mechanics packrat who loves using tables and charts from one system while running another? Show us some of your mojo!

webtech's picture

Here is my 1d100 to AW Stats conversion table...

1d100 AW10 AW7
01-03 = -2 = -5
04-09 = -1 = -4
10-17 = +0 = -3
18-28 = +1 = -2
29-42 = +2 = -1
43-59 = +3 = +0
60-73 = +4 = +1
74-84 = +5 = +2
85-92 = +6 = +3
93-98 = +7 = +4
99-00 = +8 = +5

· If you have a % skill score between 29 and 42 (inclusive), that translates to a +2 on 2d6 where 10 = success.
· +4 is the highest (and -2 the lowest) you typically see in AW, but I included higher and lower mods just because.
· If you have a +2 in AW terms, this is the same as saying "roll 42 or lower on 1d100" (for a Full Success).
· Note that the row for partial success (AW7) is always 3 rows down from full success (AW10).
· The numbers are very close to accurate; the margin of error in this 3-row-jump is only +/- 1% in the worst cases.

How to use this:

To import a 1d100 skill/stat into an AW game:
· Consult the row for your 1d100 %score and look under the AW10 column. This is your AW mod for that roll.
Example: A PC with a %score of 42 would have a +2 mod for that skill/stat in an AW game.

To import a 1d100 action resolution roll into an AW game:
· Consult the rows for your AW Stat under the AW10 column (Full Success) and the AW7 column (Partial). The high-end of the range shown is the number you must roll lower than.
Example: A PC with a +2 needs to roll below 42 for Full Success, and anything from there to 84 is a Partial Success.

To import an AW move into a 1d100 game:
· Hitting your %score or lower is a Full Success (10+); hitting within 3 rows down from there is a Partial Success (7-9).
Example: A PC with a %score of 42 needs to roll below 42 (ie hit on their score) for Full Success (10+ result), and anything from there to 84 (3 rows down) is a Partial Success (7-9 result).

Paul T.'s picture

A long time ago, I was involved in a project to put together a proprietary game system for a game company, which it could use to publish all of its stuff, along with conversion notes to popular systems. The idea wasn't to make a great game (perhaps no one would ever play that game, after all!), but to make something that served conversion well.

It was a fun project, and, in the current design climate (nearly 20 years ago), it made a lot of sense. These days, with game design becoming so much more varied in form, it seems much less realistic a project.

However, some hybridization between *particular* games is still a great idea. I'll think on it some.

I believe my conversion notes from D&D stats to AW-style rolls was one of the things that inspired the chart above; back on Story Games I found lots of correspondences between AW's rules and old-school D&D rules.

For example, I like how a lot of old-school "1 in 6" rolls convert cleanly to a PbtA/AW style 2d6+adds roll: rolling a 10+ on two dice has the same odds as rolling a 1 on a d6. That means we can convert or import all kinds of rules back and forth. A "1 in 6 roll" is like try to get a 10+ on a stat without bonus or penalty, and old-school D&D already uses 2d6 for things like Morale checks. Modifiers convert between the two pretty closely, as well - either a +1, increasing your odds by 1 point on the d6, or rolling an extra die all adjust the odds in very similar ways, so you can mix and match freely: "1 in 6, roll an extra die for each advantage" is pretty close to "roll 2d6, looking for 10+, and add 1 for each advantage", for instance, but you can mix and match in any other way you like, too.

I've always spent some time working on a PbtA-style rehash of In a Wicked Age... - unfortunately, it's not currently in a playtestable form, but at some point I might throw that together.

A fun thread or thought experiment might be to pick pairs of games and to look for conversions or correspondences.

For instance:

My Life with Master and FATE. Find the linkages!

Alexander White's picture

The pbta iawa mashup is something I'd be interested in. If you do get a playtest version together start a thread or something.

Thanuir's picture

I have mostly been converting characters, items, monsters, etc. between various editions of D&D. Also some conversions from Torchbearer and some from or to Burning wheel. Converting content is quite a different process than what is discussed here.

If I am using an adventure that specifies an obstacle, rather than checking the exact probabilities, I use one of two methods:

1. How likely is a random untrained person (average stats and so on) to succeed at this? What would be the corresponding difficulty in the other system?
2. How good does a character have to be for the probability of success to be 1/2? What is the corresponding skill level and thereby difficulty level for the other system?

Since rules scale characters differently and use different methods of rolling dice, satisfying both 1. and 2. is generally impossible. 1. works well for usual difficulties, while 2 is better for very high difficulties. (Very low difficulties are simple, since rules usually run out of granularity and it very rarely matters anyway.)