In the meantime, I wanted to rant a bit about the idea of unified game mechanics. Whether you use one mechanic to determine two different things, or a different mechanic for each, is pretty much a matter of taste, but there are still some people who insist that a unified core mechanic for all needs is the best way to go. They miss out on some good opportunities this way, since some mechanics are better for yes-no, hit-miss questions and others are better for multivalue results, or provide an easier, more intuitive way of separating ordinary success from critical success.
Take, for example, ability checks. If your game's ability scores are in the 1-20 range (or 3-18, for D&D,) then a roll under with 1d20 makes a lot of sense, even if some other checks like attack rolls use a roll over approach. Trying to switch to a unified mechanic means one of two things:
- If you opt for roll under, you need to change the attack rolls, perhaps using roll under Dex for ranged and roll under Strength for melee.
- If you opt for roll over, you need to derive new ability check target numbers for each ability, such as 21-Ability.
Or even worse, if you decide to go with roll over because "obviously" higher rolls should be better, but you want to minimize the effects of ability scores, you go with ability score modifiers such as the current D&D's (Ability - 10)/2, but that leads to people asking "Why do we even have stats? Why not just modifiers?"
And you lose the chance to make distinctions between easy and hard tasks in a simple manner. WotC D&D has been using DC tables for skill checks: Beat a score of 5 for Easy, 15 for Medium, 25 for Very Hard, with many other in-between points also defined. But do you really need that many? And even though it is simple, why not use the even simpler and more memorable system of "roll d20 under ability for most tasks, d100 under ability for extremely difficult ones"? You never need to change your target number that way.
I was re-reading the Judges Guild Ready Reference Sheets recently, since they've been mentioned in a couple blogs. They use the d100 under ability for difficult tasks, like bending bars. But since a d100 is actually a two-dice roll, they were able to use another feature: on doubles, the character's ability is strained and unusable for several days. By using a different dice mechanic for one kind of action, they are able to exploit a feature unique to multidice mechanics -- rolling doubles -- to create additional detail with no additional die rolling.
Sometimes, the slavish devotion to unified mechanics means using the mechanic even when no mechanic is necessary, or complicating rules that don't require dice rolls. My last couple posts on ability rolls made a big point about not rolling at all, most of the time, because a character's high scores made that kind of action trivial. The new D&D 5, as already mentioned, has those DC 5 rolls, which seem kind of useless. It also has "passive checks", which do not require a roll, but do require claculating passive check scores for each ability (10 + ability modifier.) Again, wouldn't it have been simpler to make the passive check score the same as the ability score, so you wouldn't need to keep track of six extra scores? Passive check scores basically exist because the WotC way insists all mechanics must be d20 + ability modifier, so if you substitute a flat 10 in place of the d20 roll, you still need to calculate the final score.
And the sad thing is, it still is not really unified. The damage mechanic is still one or two dice of several different varieties, instead of being based on a d20 roll. It's OK to have variety there, apparently. Because, as I mentioned at the beginning, it really is all a matter of taste.