Alternate Dice Interactions

I like playing around with dice. Figuring out probabilities and how they'll change in different circumstances is fun. It's one of the reasons I used to write systems, they let me implement my weird dice ideas and see how they worked. I'm more focused on writing content these days, so I figured I'd share the interactions I haven't gotten around to using yet. They might as well see the light of day now and instead of waiting for some nebulous future game.

Dice interactions are rules that directly interact with the math of a die roll to alter the outcome in some way. Some common ones most folks are familiar with are:

- Being able to reroll
- Replacing a roll result with a pre-rolled value
- Bonuses and maluses
- Advantage and disadvantage

Anything that modifies the dice rolled or the roll's result counts.

Here are some interactions I'd like to see used widely one day:

Step Up/Down

Alter what size die gets used in a roll. Make an ally's d4 roll a d6, or an enemy's roll use a d12 instead of a d20. (This one's already used regularly, but not enough that I'd call it common. I want to see it used even more often.)

Twin

Add a second die of the same size to a roll, turning the linear probability into a triangular distribution. There are already spells and abilities that let you add a specific die size to your rolls to give a variable bonus, but this is more about creating the curve probability than just providing a boost to the roll's result. It lets the player choose to avoid the risk of rolling very low or high and increase the probability of mid-range values. A play it safe strategy.

Pool

Add multiple dice of the same size and turn a single-die roll into a pool. Exactly how many dice are in the pool could be determined based on level, abilities, spell effects, whatever. It's not important. What's more interesting is how to resolve a roll like this. A number of successes-based threshold doesn't make sense for a roll that likely originally had a target number to beat for resolution. The two options that make the most sense to me are:

1) The result is the total of the dice. So a pooled skill check would (likely) have you rolling Xd20 and a pooled damage roll would be Xd[damage die]. It could easily end up being overwhelmingly powerful. It would also have the same mid-range stabilizing effect as Twin since it introduces a bell curve. The more dice you add, the more centralized the curve.

2) The result is one value chosen out of the separate rolled values. So if you roll a pool of 3d20 and get 2, 14, 9, only one of those is your result. There are a few ways you could decide which of the values is chosen. The most obvious is to pick highest or lowest, but that would just make this Advantage/Disadvantage with more dice. That's boring. The better option is that the player chooses which of the values they want to use.

Bulk

Replace the lowest value on a die with the highest so the highest value's probability is doubled. (Ex: On a d4 you'd replace the 1 with a 4 so your possible outcomes are 2, 3, 4, 4.)

Sap

Replace the highest value on a die with the lowest so the lowest value's probability is doubled. (Ex: On a d4 you'd replace the 4 with a 1 so your possible outcomes are 1, 1, 2, 3.)

* The probabilities for Bulk/Sap are different from Advantage/Disadvantage. The -vantage rolls are independent, meaning you still have a 1/X chance of each possible outcome in each roll. For Bulk/Sap the highest/lowest value has a 2/X chance of occurring. The significance of the 2/X probability also changes with the die size and has a much more dramatic effect on smaller dice.

Cycle

Rolls don't have a set die they use. Instead you cycle through the dice in a standard set, either stepping up or down with each new roll. So if you start a session rolling a d20, your next roll will use a d12, then a d10, a d8, d6, then after you roll a d4 you cycle back to a d20.

You can alter the direction of the cycle at any point with abilities/spells/etc to do things like making an enemy go 8-6-4 then reverse direction to 6-8-10 order instead of looping around to 20, or timing it beneficially for an ally.

Spiral

For enemies only. Each time they succeed add a die to their rolls so they have an ever-growing dice pool. The more they succeed, the more likely they are to succeed in the future in a self-sustaining spiral and get more dangerous as time goes on.