A dice pool refers to a resolution mechanic where rather than rolling a dice or a number of dice and summing the results, the number of dice themselves is some part of the mechanics. The simplest version of a dicepool is one where you roll a large group of dice, and then select which results apply to which part of the resolution.
A single dice (or number of dice plus a modifier) is a resolution mechanic that follows a very simple experience: You roll the dice, you do the math, and then you have your result. This makes a dice roll, singular, as a very simple ‘switch’ experience, comparable to pushing a button in a videogame. You press a button, the system responds to the math, you get a result. That’s a really good, robust mechanic I like using for any game where you want some variance in a reliable, regular action – like in D&D, for example.
A dicepool, by comparison, is more of a system for making resolution itself a game. This isn’t all it’s used for! But it’s a simple way to use dice that isn’t just adding or subtracting on top of them.
So one of the most basic things you can do with dicepool systems is you can make players make decisions. Let’s say you have a system where players are setting up a car for a race. You roll a fistful of dice at the start of the game, and select, of those dice, some to be the engine, some to be the tires, and some to be the seating. Then, as you play the game, you prioritise how you drive your car based on those earlier decisions.
One way that Exalted uses a dice pool is that you roll your d10s, and all dice that are 7s or higher are ‘successes,’ and you need a certain number of successes to win. This is a weird bit of terminology that maybe a designer who cared about language might fix but whatever, like in Blades in the Dark the point is that you can use a dicepool to handle a resolution in a system where you want players to succeed, on average, but don’t want the degrees of success to be as varied as the numbers on each dice face.
A dice pool doesn’t even need to be rolled: You can use a dicepool system to have a number of counters that are kept at a particular number, or incremented as appropriate, based on the players’ choices. And even then you can use that these counters are dice as part of the play: Make it so it’s calibrating a computer, and sometimes a virus rolls some of the dice randomly!
Dice pool systems can get pretty weird when you make them success-or-fail. It’s also got a mechanical limit – rolling 1d20+30 is not the same physical question as asking someone to roll 30d6 and count the successes.
Another thing with dicepool systems is that when you add components per player, they get out of hand fast – so if you want a game where each player needs to roll 5 dice, then one player needs 5, and 2 needs 10 but if you wanted 4 players you need 20, and you need to store those dice.
One final thing with dice pool systems is that while rolling big fistfuls of dice is exciting, doing fiddly book-keeping or rules changing or changes to each dice in the pool multiplies irritation. So it doesn’t always work with every type of dice mechanic.
Exalted, Scion, and the other of White Wolf’s other various roleplaying games.
Blades in the Dark.