I'm looking for a dice mechanic that supports a particular type of realistic feel. In particular, I'd like to find one where any task could potentially be rolled for without generating absurd results either alone or when bonuses or penalties are applied. The most common problem I observe in this regard is that games have a sweet spot where everything works well, and then you try to apply them to very very easy tasks and they fail horribly (e.g. I can run down a flight of stairs with much, much higher probability than 95%) or to very very hard tasks which become impossible or do not get as difficult as they should. Players try all sorts of crazy things, and allowing players to take control of really easy things can be helpful at avoiding silly deus ex machina events.
So, with that as preamble, the real criteria are as many of the following as possible:
- A wide range of difficulties can be represented (up to anything that could reasonably happen by chance in years of gaming--if you can play for years and never succeed, then the GM (or the mechanic itself) can just say "no, never")
- A wide range of trivialities can be represented (down to anything that might fail just once in years of gaming).
- Bonuses and penalties feel about as significant when they occur during very difficult or easy tasks as they do for "normal" challenging tasks. (Counterexample: a +1 bonus taking 20 to 19 is a lot more significant than taking 11 to 10 on a 20-sided die.)
- You have to actually be able to do this with real dice in a not-outrageous amount of time.
The systems that I've used that come closest use some sort of exploding dice mechanic, but all of these that I know of fail the sensible triviality test, and often have other weird quirks (e.g. Shadowrun 2-3 handles difficulty well with exploding dice, handles triviality poorly for non-expert characters since 1 on 1d6 is always failure, and non-experts get very few dice to roll, and has strange wrinkles for bonuses and penalties--changing 5 to 6 is huge, but 6 to 7 is nothing).
It's been quite a few years since I've looked at what games are available, so maybe something new has appeared, or maybe there's an older game that has these properties that I never stumbled upon in the 90s. Or something never published in any game, but which works like this--a lot of times it's not that hard to retrofit game mechanics. I'd like to be able to tell players, "Look, don't roll for trivial stuff. But if you insist, go ahead." Or, alternatively, if they're relying upon something easy that isn't utterly trivial--e.g. if they start relying upon the master archer to be able to put the arrow in an invading goblin's eye every time --then I would like to be able to tell them, "Well, okay, but you're going to have to roll," mostly as a mechanism to get them to think about some other approach than taking a holding pattern where adversaries are powerless to touch them.