Well it looks like ForeSight Second Edition might just be published soon, and my thoughts are turning to the, perhaps unenviable, job of marketing a game firmly based on percentile dice (also known as D100): i.e. a pair of dice which when rolled give you a random number from 1 to 100.
The D20 juggernaut is basically a D&D thing. It’s not clear whether it’s an effort to keep third-party dice manufacturers happy, or a plot to convince people that the morasse of special cases, tables, and bizarre rules that constitute D&D is in fact a “system”. In any event, my reasons for eschewing D20s are technical, much as my reasons for eschewing 3D6 (as discussed earlier).
In any role-playing game there tend to die roll ranges for which exceptional outcomes are assigned. For D20-games these are rolls of 1 and 20. In other words, 10% of all resolution rolls (cases where a die is cast to determine what happens in a situation) result in something outlandish occurring (e.g. an automatic success or failure regardless of the odds).
Shit happens. But should it happen 10% of the time?
Now, in action movies and similar genres from which RPGs tend to take their cures, shit does indeed happen 10% of the time. But unfortunately, the 10% of the time we’re talking about is actually a gross understatement.
For example, a mid-level warrior in D&D will swing his/her sword three times in a single round of combat, which means he/she has three chances to have shit happen. If he/she is fighting a similarly capable opponent, that’s another three chances to have shit happen.
(For the statistically inclined, that’s a 1 – (0.9 ^ 6) probability of shit occurring in a single round — a few seconds — of combat, or roughly 47%. Most fights last several rounds. If this were a movie, this would be like half of fights having something ridiculous happen, such as someone trip over their feet or hit someone in the eye with a lucky shot, the moment a fight started.)
In RuneQuest 2nd Edition, a D100-based system, there were various tiny percentage chances of shit — things like a warrior slicing his own head off — happening every time someone did something. Of course when you did the math (and an article along these lines was posted to Murphy’s rules) you ended up with ridiculous results: in a battle of 1000 warriors lasting five minutes, some insane number would decapitate themselves, some far larger number would chop off their own limb, and so on. In each case the results were simply constructed by taking (1 – probability of ridiculous outcome) and raising it to the power of the number of times the dice would be rolled (50 for ten minutes of RuneQuest combat) — and that’s the probability that you will escape that ridiculous outcome.
When the probability of an extraordinary outcome is 10%, you know you’re in big trouble.
Of course, the extraordinary outcomes in D20 can’t be too ridiculous or the system would seem obviously broken. Instead they’re just low key enough to have lots of silly effects (e.g. because armor does not block damage but instead reduces hit probability, and because a roll of 20 is always a hit, a huge number of tiny attacks will automatically kill someone in plate armor) while not giving the feel of “critical hits” (the finest archer cannot kill a healthy 10th level paladin with a single ordinary shot) while neither implementing any concept of “degree of success” nor producing genuinely unexpected results to create drama.
Before I start rambling too far, I will mention one funny thing. D20 system is in fact D20 + D12 + D10 + D8 + D6 + D4 system. The D20 games rely on a ridiculous set of dice and use them to achieve an unnecessary level of granularity (a weapon either does D6 or D8 damage, nothing in-between).
Anyway, here are two possible slogans for D100 System games.
D100 System. Shit happens, but not 10% of the time.
D100 System. You already have the dice.