Some progress on my Dr. Jekyll-inspired tabletop RPG design for the #RPGenesis game jam

(This post is Cross-posted from the #RPGenesis jam forum on itch.io)

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.