As I mentioned in the introduce yourself thread, I'm working on a game set in the world of the story "Strange Case of Dr. Jekyll and Mr. Hyde" by Robert Louis Stevenson. The PCs will all be people in Victorian London who are studying this new and disreputable science of nature/essence manipulation because they think it's the way to address some personal drive that can't be satisfied by conventional means. I don't have a title yet. I think referencing the original story is probably a must, but I haven't settled on anything I'm totally happy with yet. Right now I'm thinking of something scientific-sounding that refers to Jekyll's experiment or process, or that these people are working in the same field as Dr. Jekyll. So something like "The Jekyll Conjecture", "The Jekyll Process", or "The Jekyll Hypothesis", or something along the lines of "Jekyll's Contemporaries" or "Jekyll's Colleagues". I'm open to suggestions if people have any.

Mechanically, characters are going to have a bundle of freeform traits called "essences". So you might have essences like "strong", "precise", "arrogant", "greedy". Eventually there will be mechanics related to manipulating these essences directly (enhancing, suppressing, extracting, inserting new ones, etc.) but I haven't written those yet. Basically I want Jekyll's potion that turned him into Mr. Hyde to be something that you could duplicate with these mechanics if you were so inclined, once you had figured out the chemistry of how to make it.

This morning I made my first attempt at writing out some dice mechanics. Here's what I have so far:

Rolling the dice

When the mechanics call for you to roll the dice, the GM will compare your essences to the task at hand.

First, they'll figure out the strength of your positive dice by identifying the most apt essence for what you're doing. For example, if you are performing surgery your precise essence might be the essence that seems most apt. The strength of this essence will determine the size of your positive dice from among d4, d6, d8, d10, and d12. Add 6 to the strength of your apt essence, and find the biggest die that couldn't roll higher than that number. So if your precise essence had strength 5 then you would be rolling d10s [6 + 5 >= 10], but if it was strength 6 you'd be rolling d12s [6 + 6 >= 12].

Second, they'll figure out the strength of your negative dice by identifying the essence that's most opposed to the action. For example, while performing surgery your impatient essence would be running counter to what you were trying to achieve. The strength of this essence will determine the size of your negative dice from among d4, d6, d8, d10, and d12. Take 10 and subtract the strength of that opposed essence, and find the biggest die that couldn't roll higher than that number. So if your impatient essence had strength 3, you'd be rolling d4's to perform the surgical procedure.

The process of identifying an apt and opposed essence must find one that are genuinely aligned or opposed to the actions. All humans are considered to implicitly have every essence at strength 2 in addition to whichever ones are tracked on your character sheet, so in the worst/base case scenario you'll have a strength 2 essence for your apt and opposed essences if none of your explicit essences seem to apply.

Third, the GM will go through each of your essences and decide whether it's a positive essence for the task, in which case you'll add a positive die to your hand, a negative essence for the task, in which case you'll add a negative die to your hand, or a neutral essence for the task in which case it won't contribute dice. You'll roll at least one positive and one negative die for each roll, in the case where your explicit essences don't seem to apply (for example, perhaps all your explicit essences seem positive or neutral) one of your strength 2 implicit essences will contribute a die.

Finally, you'll roll your handful of dice and compare the result to the target number determined by the mechanics for the type of roll you're making (which will usually be set by the type of scene). In general, dice that get results greater than or equal to the target number will result in achieving some degree of success at the task you were trying to achieve, while dice that roll below will often result in the accumulation of stress or complications.

Note: The rules give the responsibility for analyzing your character's attributes to the GM. This is because you may not be aware of the strength or exact definitions of your own essences! In a game where you might be experimenting on yourself with brand new techniques that can alter your essences you won't always have perfect information about your own character. Dr. Jekyll discovered what it was like to be Mr. Hyde by being Mr. Hyde. Of course there are mechanics that can help you determine the strength of someone's essences, and you can certainly use those mechanics on yourself if you are so inclined.

I'm a little concerned that this will be clunky (and this is already my attempt keeping things streamlined). I'm trying to have both the strength of essences and which essences you have be relevant to your rolls. But having lots of essences and them all having numbers attached might be too much. In the original story, the fact that Jekyll had powerful urges toward both goodness and sin were issues with him -- his opposed nature was getting in his way no matter what he was doing, but once he suppressed some of the more noble parts of his character he was able to fully enjoy himself as Mr. Hyde (which had the surprising effect of making him less burdened by stress as the full person of Dr. Jekyll so he was more able to do good works in that persona). So I'm hoping to capture some of the spirit of that in the mechanics.

Here's my first attempt at the "Science" subsystem.

Creating the Science Matrix

Before the game begins, roll 8 d4's for each row of the matrix. Count up the number of dice that correspond to the column number, add 1, and put that number in the cell. So, for example, if you rolled [3, 4, 1, 1, 2, 3, 4, 1] for the Surgery row, you would fill in 4, 2, 3, 3. For the MISC row, add 3 rather than 1 to the d4 roll.

The science of essence manipulation

This science is still a very new field. Not much is known about it. Indeed, the results of Jekyll's experimentation are about the only thing that is known for certain. To wit, a certain chemical mixture, when ingested, enabled Dr. Jekyll to suppress certain essences which he considered his “good side” leaving only his “evil side” active. The change affected both Jekyll's personality and physical form, although his memories remained intact across transformations. The duration of the effect eventually became erratic, with the transformation sometime ending on its own, sometimes requiring another ingestion of the mixture to reverse, sometimes happening spontaneously in the Jekyll form. However, even Jekyll himself was not fully aware of how to replicate his process; before his death he determined that an unknown impurity in his initial batch of formula was a key component in its efficacy.

In order to maintain the spirit of empiricism, players of this game will never know for sure how things work. The functioning of this field of science will partly be determined by a dice-rolling procedure that the GM conducts before play begins. The GM keeps this information secret from the players while the game is in progress. By conducting experiments players, like the characters they control, may gain some insight into the way the science functions, but science never provides certainty, especially in such a new field. Jekyll thought he understood what he had discovered, but he only partly understood. On the other hand, those who never dare to explore understand nothing at all.

In order to “explore” the science of essence manipulation, the GM must make a virtual “map of the territory” before play begins. This takes the form of a large matrix. The rows of the matrix correspond to aspects that might be involved in an essence-manipulation process. The columns are abstractions that represent that some things work better than others.

When a player wants to develop a process they'll describe what they're trying to do, and map that onto a series or corresponding matrix cells. For example, if Dr. Jekyll were a player character, he might have said that he wanted to create a chemical mixture that would operate inside a person's body to target a particular subset of essences and reduce their strength to zero. For each major category you roll a d4 to see which column of the matrix it uses. So, in game mechanics terms, Jekyll's formula could be CHEM3-BODY2-DEC4 (the numbers correspond to random d4 die rolls). Someone else might propose a process by which a person's blood is extracted, heated under intense pressure, and then reinjected into the body in order to increase the strength of an essence. This could be FLUID3-ENV1-FLUID2-INC1. Then roll a d6. If you have less components in your process than the number on the d6, add MISC components to the process (sometimes it turns out to be harder to create elegant processes than ones that might seem complex on the surface).

Once you have the sequence, the GM will add the numbers in each cell of the matrix to determine the difficulty to compare to the die roll in a Devise a process scene. If the numbers are low this sum may correspond to a simple task that's merely waiting for someone to try it for the first time. If it's difficult perhaps it's possible, but requires some expertise to perform the required delicate procedures to get the right efficacy. Some may be so difficult that they're effectively impossible to do that way – sometimes science doesn't care how much you'd like to achieve something, it just can't be done (just ask the alchemists who hoped to turn base metals into gold). However, the GM will never tell any players what the actual difficulty number is. The only way to know for sure is to experiment, and see if the results are what you expect them to be – if your mechanical roll to invent the procedure is lower than the difficulty number the GM may alter the actual effect relative to your intended effect based on some rules. Sometimes this might be as simple as being fatal to whoever is being subjected to the process, sometimes it might be subtle, such as the intended effect working perfectly but a second essence being redefined as a side-effect. Regardless of the relationship between your roll and the difficultly number, the process (if performed correctly) will always “succeed” at producing the same effect in the future. Maybe a mistake in one area could be a serendipitous solution for another.