I thought I would talk a little bit this week about our decision to not use opposed rolls in the Infinite Earths Roleplaying Game.
The core resolution mechanic of a d20 game is elegant and simple – roll a twenty-sided die, add in any relevant bonuses from training and natural ability and compare the result to a target difficulty number. If your result is equal to or greater than the target number, you succeed. If it is less, you fail.
That’s why opposed rolls have always struck me as an odd design feature in d20 games. Players still roll their d20, adding in the same bonuses. But instead of rolling against a set difficulty, the Player’s result is compared against the results of a second die roll. That roll also is modified by the training and skill of the Player’s opponent in the situation.
At first glance, opposed rolls make a certain degree of sense. It’s an attempt to simulate that two different things are being tested at once. But that view doesn’t hold up with the way the rest of the d20 system is designed.
Take a look at attack rolls. Two different things are happening – one character is trying to hit an enemy while that same enemy is trying to avoid the blow. Only one d20 is rolled here – the check to see if the attack hits. That’s because the d20 system is built around the assumption that the defender’s die roll is the average result of 10. That’s why armor class starts from a base of 10 and most difficulty checks are against numbers of 10 or higher.
Since d20 only uses opposed roles occasionally, those situations can start to feel arbitrary over time. Consider this odd situation: If a character comes across a barred door in a dungeon, he rolls against a static difficulty number to determine if he can force it open. But if the person who barred the door is standing on the other side holding it shut, two dice are needed to determine if the door can be opened.
This has a few negative effects that we do not want to include in the Infinite Earths system. First, it’s an exception to the rules. Exceptions tend to slow things down over time. Exceptions also make it more difficult for players to learn a game. We want Infinite Earths to be as consistent as possible so players can focus on what they are doing, not wonder what they should be rolling.
Secondly, opposed rolls can take more time since more dice are involved and the special rules for that situation have to be taken into consideration (such as how rolling a natural 20 or a natural 1 interacts with opposed rolls). We’re trying to cut out special rules for limited situations to minimize the need to look things up during play.
Third, opposed rolls can make outcomes much more random. If a Player gains a +1 to a d20 roll, then he knows he is 5 percent more likely to succeed. There’s no such assurance when making opposed rolls, which makes it more difficult for Players to know the odds. For Infinite Earths, we want Players to be able to judge just how likely or unlikely they are to succeed at something.
And that brings me to how we handle Stealth, Sleight of Hand and perception in general.
Many d20 systems make the classic rogue character a master of skills, often awarding far more skill points to that class than any other. But those skills often are forced to be opposed rolls instead of standard skill checks because of these exceptions. This means even a good or better-than-average Stealth roll might still fail because of random luck from the opposing roll.
That’s why all Stealth and Sleight of Hand checks in Infinite Earths are against a static difficulty number. The base difficulty of such rolls is 10. The Guide then adds modifiers based on the most appropriate conditions affecting the roll using a standard chart. These conditions are divided into distinct categories such as Lighting, Noise and Concealment. Sneaking through a battle is much easier than creeping through a quiet house. Hiding is much harder at high noon than twilight. And avoiding a direct line of sight is a great way to dramatically reduce the difficulty of the roll.
Calculating the target number of a Stealth or Sleight of Hand check can take a little longer than some other skill checks. But it puts a great deal of power in the Players’ hands since they know the modifiers and the odds. Waiting until the guard has his back turned will make things easier. A noisy distraction nearby is another way to make a Stealth check more likely to succeed. And since the modifiers are part of a standard chart, Players and Guides are working from the same ground rules for how the skills work.
This also means that there are no perception rolls of any kind made in Infinite Earths. This has had an interesting effect on playtests so far. Players who want to find a thief hiding in the shadows light a torch and start looking around or simply tell everyone to be quiet for a moment. That’s because a hidden character must make a new Stealth check if the conditions of his or her hiding place change (and this new check is against the new difficulty).
As a result, those who want to find hidden characters must actively work to flush them out rather than standing in one location and rolling perception checks until luck finally tilts in their favor.
Not having perception skills also helps avoid the temptation to make players constantly make rolls just to interact with the environment the Guide describes. It encourages interaction, as well. Those who want to overhear whispers need to figure out a way to get close enough, rather than invest more skill points. This also removes the need for most characters to invest in perception-like skills as a passive, secondary defense against would-be assailants. Skills really aren’t meant to be combat attributes in this system.
Are opposed rolls bad? Certainly not. But it just doesn’t quite seem to fit when it’s a different resolution mechanic than everything else in the game.
Ultimately, we hope this makes skills more equal with each other by making them a measure of what characters can do rather than a defense against what might be done to them.