Easy way to (sort of) do percentage resistances

[NichG]

Division and fractional multiplication slow a game down, so I've always avoided them in design. But fractional resistances have a lot of nice properties compared to flat reductions (like remaining equally relevant at different power levels, avoiding unintentional 'you just can't damage this' situations, etc).

It just occurred to me recently that if you structure all your scaling damage as 'extra dice' rather than dice+modifiers, it's easy to do fractional resistances as 'reduction per die' - each point would correspond to 1/sides resistance. It also would mean that something increasing or decreasing dice size corresponds more directly to changing the degree to which a damage source penetrates resistance - you could have environmental damage be d2s and d3s, particularly intense forms of energy be in the form of (fewer) d12s or d20s. Flat plusses would be reserved for damage that absolutely bypasses resistances, so you'd want to make those more special and not just have e.g. dice+stat mod damage lines.

Probably best to not do the reduction calculation independently on each die (would mean you have to count the damage pool multiple times if hitting things with different resistance values), so it's basically just 'reduction = resist * pool size).

Anyhow, it's kind of obvious in retrospect, but seemed like a nice design trick.

[Rilmani]

I do believe you’re exactly correct, and I’m surprised I haven’t seen this in another game system. Seems superior to percentages. So some examples:


1. Creature with Resistance 1/6 (1d6) takes 13 damage. 13 can be divided by the denominator 6 twice, which means we multiply 2 times the numerator, 1, is which equals 2. Creature blocks 2 of 13 damage, 13 - 2 = 11 damage taken.
2. Creature with Resistance 3/4 (1d4 showing “3”) takes 30 damage. 30 divided by 4 equals 7. 7 multiplied by 3 is 21. 30 minus 21 results in 9 damage taken.
3. Creature with Resistance 1/10 (1d10) takes 9 damage. 9 divided by 10 is less than 1. Creature takes 9 damage, 0 is prevented.


This mechanic could be expanded. “Increase/Decrease your Resistance Die by one step” would work like the following d20<->d12<->d10<->d8<->d6<->d4.
“Roll your resistance die at the start/end of your turn” or “as a reaction after taking more than X damage” would change the numerator in the above fractions.

The only grey area would involve attacks that deal multiple kinds of damage, like weapon attacks amplified by Smite. That could really slow the game down. Or the source of damage needs to declare one damage type from the included sources which will be used for *all* damage inflicted from said effect.

[Anonymouswizard]

It's also a relatively elegant way to do armour penetration, assuming you don't want to do it realistically. If armour was rated per die then weapons good at piercing armour use fewer but larger dice. This'll also tend to make them average lower but swing more, but if you balance around the average weapon dealing three dice it might not be particularly notable.

As a side note, this makes anything doing 1dX+Y damage incredibly strong, you basically ignore armour but still do reliable damage. Modifiers should probably be kept small compared to the die size or else players will end up gravitating towards static bonuses over extra dice.