So here’s a weirdly prevalent thing in RPG design circles: Someone will ask for feedback on their new weird dice system. They won’t provide any context, like what their system is about, or who their PCs are, or what they’ll be doing on an average adventure, or whatever. They’ll just present their dice mechanic and ask if it’s any good. The answer is basically no. Your dice mechanic is never good, because the presentation alone is a huge red flag that you have no idea what a dice mechanic is even for. I’ll explain below the break.
The purpose of a dice mechanic is to inform how much of a power gap there exists between different characters (player or non-player) in the setting. That’s it. That’s the beginning and the end of it. Some of them can do this in really novel and unusual ways, but in the end a dice mechanic governs what it means to have a +1 bonus to something and that’s it. In a d20 system, having a +1 bonus always means you are 5% more likely to succeed. In a d100 system, having a +1 bonus always means you are 1% more likely to succeed. In a 3d6 system, having a +1 bonus means you are 12.5% more likely to succeed at tasks that were a 50/50 gamble otherwise, but <1% more likely to succeed at tasks that were basically a foregone conclusion in the first place, whether that’s a foregone success or a foregone failure. A d20 and d100 system both allow you as a designer to be absolutely certain of what a +1 bonus will do in any circumstance. Of the two, a d100 allows for tons of tiny +1 bonuses to eventually add up to something. With a d20 just three +1 bonuses (or one +3 bonus) will make a noticeable difference in success and failure rates, but getting the same effect out of a d100 requires no less than fifteen different +1 bonuses. This means that a d100 system can hand out +1 bonuses like Halloween candy and so long as they aren’t situational (which would get extremely hard to remember and track) it’s fine.
A 3d6 system’s bell curve means that every last bonus will be critical in the most decisive die rolls, but it still takes a nearly as large bonus as on the d20 to be so far ahead of the curve that your success is guaranteed even on the lowest die roll of 3. For a 3d6 system, a +1 bonus is something you definitely notice, but it still takes a +15 to be guaranteed success against a TN of 18, the highest you could roll with no bonus at all. So the advantage of a 3d6 over a d20 is a +1 bonus makes a big difference but it still takes a huge total bonus before the roll is literally a foregone conclusion. Except that can also be the 3d6’s disadvantage, if you want to be able to hand out a few tiny bonuses that slowly add up to big ones. Remember, in d20, a +1 bonus is so small that it’s almost never the difference between success and failure, so you can give out three different small circumstantial bonuses and have them add up into something significant. In a 3d6 bonus, every circumstantial bonus is potentially decisive, so there’s no such thing as a small bonus.
In a dicepool a +1 bonus will give you a certain fraction of one hit on average, depending on what dice are in the pool and what each one needs to get a hit. In a Shadowrun style pool where you roll d6s and get a hit on a 5 or a 6, a +1 bonus means you will get 1/3 more hits on average. If you’re rolling d10s and get a hit on a 6+, a +1 bonus means you will get 1/2 more hits on average. This means that the total odds of success can keep climbing, but the chance of failure is never completely eliminated, which is good for modeling relatively gritty and realistic scenarios where the underdog always has a chance and bad for modeling high fantasy or super heroic stories where the weakest character’s best efforts are outshined by the strongest character’s worst, i.e. where a random NPC civilian has basically no hope of defeating an ogre but high-level adventurers can fight them in droves. For a cyberpunk system like Shadowrun, it’s more useful to say that tossing a sidearm to some random schmuck on the street still gives him some chance of shooting and killing a powerful street samurai, which means that just like in real life having a large number of people is always a critical advantage, which means that just like in real life the biggest problem in security is figuring out how to get a relatively small security force to a point where they can drop 8+ guards on any location in the whole facility, and in turn the biggest assets for an infiltrating force are stealth and speed, not the ability to kill each individual enemy in the entire dungeon.
If you’re doing the thing White Wolf used to do sometimes where they’d add bonuses to the target number on a d10 dice system, that means you wil get 1/10 more hits on average per die in your pool, which means characters who already have large dice pools get a huge bonus (possibly more than a full hit on average) and characters who have small dice pools will barely even notice. The math gets even more complex if there’s botches or glitches or whatever, and generally speaking the more weird qualifiers you have on a dice system, the harder it will be for you as a designer to predict how it will work in advance, and the more likely it is to break down and do something stupid in actual play. In fact, let’s go ahead and put that in bold, since it’s the first important thing we’ve discussed so far: The more weird qualifiers you have in a dice system, the harder it will be for you as a designer to predict how it will work in advance, and the more likely it is to break down and do something stupid in actual play.
Which brings us to really weird stuff like the Edge of the Empire dice pool system, where there are different shaped dice and instead of numbers they’re stamped with special symbols that mean different things. You can have a success, which is just a hit with a more confusing name, an advantage, which gives you a special benefit of some kind (and usually you need a set of two or three to get any benefits you really care about), or a triumph, which gives you a critical effect. Instead of requiring a certain number of hits, one hit is always a success, but your hits and advantages can be cancelled out by failures or disadvantages rolled by an opposition dice pool, and you can also receive a despair, which gives a critical miss effect, but does not cancel out a triumph. Also, you can get triumphs on a failed roll and despairs on a successful one. We haven’t even gotten into how each of the three different shapes of dice you can have in your pool (or in the similarly constructed opposition pool) all have different odds of rolling any of these three effects. Two things to note here: First, the EotE designers have made an extremely complex system which means that doing all the math to make sure it works right is a goddamn nightmare. Second, their weirdly complex dice system is also by far the most common criticism of the game. So they did a bunch of work to make something that no one actually wants. Here’s our next important lesson I’m putting in bold: Players don’t want new dice systems, they want something they already know how to use.
The ultimate point of all this explanation, however, is that dice systems accomplish things. Their purpose is to produce specific results, not simply to function at all. The first red flag for most dice systems presented is that they are presented without any explanation of what the system is for or what it’s supposed to model. It’s like posting stats for a modern combat system without letting us know whether it’s meant for a super hero system where the rifle alone is an NPC mook weapon (although it can presumably be used with lots of special abilities if you’re playing the Punisher) or a gangland system where it’s one of the most powerful weapons available or a military action system where it’s the standard for both PCs and their enemies or what. People who post their dice system usually either have objectives that are just as easily accomplished by another, more simple system or else have objectives the system is counterproductive for. People will post their weird new take on dice pools and say it’s for a heroic fantasy system where the PCs start as particularly adventurous farmers and end as dragonslaying heroes. People will post completely bizarre, way too complex and finnicky systems and say that it’s for some bog standard setting with some bog standard premise and they expect that their dice gimmick will set them apart. In other words, their selling point over nearly identical systems that tell the same kind of stories is that it is harder to learn. A similar problem comes when people design a system around a die (d12, d4, whatever) that is infrequently used, or in other words, they design their system around dice that players are unlikely to have in large quantities specifically because they are unlikely to have them in those quantities. It’s difficult to imagine how any single design decision could be more wrong.
Even design systems that are intended to accomplish something specific and to actually accomplish that thing show clear signs of either the system having been designed first, and then excuses for what it accomplishes being appended afterwards, or else the system having suffered from hideous feature creep. In both cases, the system is something horrifically unwieldy. This is the problem that EotE’s system suffers from, and remember, that dice system is extremely unpopular and has undoubtedly lost more players than it gained. It was used by a professional developer, but that doesn’t make it a good idea. It just means we’ve seen people hate it on a large enough scale to know for sure that it was a bad idea.
Pick a dice system based on what your RPG is supposed to accomplish. 95% of the time, an existing system will work fine for it, and the barrier of entry for playing your RPG will be that much lower. Don’t make a weird gimmick dice system and then design your RPG around it. 95% of the time, all this accomplishes is making the system harder to learn.