Musings: Dice Roll Mechanics

 Dice Rolling

Usually when you roll a die in a game you want the highest result. It makes sense, doesn't it? Of course you want the highest number, it feels good to nail that perfect roll. But here's a question: What if rolling the lowest number was better? Something that comes to mind is Thac0, where having negative AC is actually really good. Thac0 is perfectly viable, but not very intuitive. Let's also look at a general system that relies on lower dice rolls before delving into a Thac0 introspective.

 Warning: Math ahead

Lower Dice Rolls

Let's say you're playing a wizard wearing light armor. Instead of having 10 + your Dexterity as your AC, what if it was 4? As in a d4? Then someone attacking you would need to roll a 4 or higher to hit you. That significantly reduces the math needed for players and dungeon masters, and makes more use of all your dice instead of relying on the d20 to determine everything.

I really enjoy the idea of using other dice like this, but I'm not quite sure where to go with it. I know a few systems use it, but it can be challenging penetrating all that information just for a little bit of comprehension how it works. (Or maybe I'm lazy. Probably that.) Let's delve into this AC vs attack a little more.

Let's say you have shitty training with weapons, so your attack is 1d4. Thus you have a 25% chance to hit a wizard. But let's say you are "decently" trained in that weapon, so you get to roll a d6 for the attack instead. I believe the math is 1 / 6 = .016, or 16% chance to roll any number. We need a roll of 4-6, so 16% * 3 = 48% chance to hit the wizard. That's nearly double your chance. But what about higher levels of AC? If your AC was 6 for wearing say... light armor,  you'd never be hit by a weapon with less than a d6. What if light armor was instead 4 + 1? In terms of mechanics this truly feels like light armor, especially when faced with a greatsword (With a hit die of say d12), you'd be decimated, just as you would expect to be in real life when wearing padded armor.

Here's another interesting idea: What if touching someone was always a d4 unless they were wearing light armor? Or trained in Acrobatics? Instead of calling it touch, we'll call it Target DC (Target Difficulty Check), because you're targeting the body and not trying to bypass its armor. So say someone with Acrobatics has an Attack AC of d4 but a Target DC of d10? The system would need to cater to a reason why you would want a very high Target DC. Maybe a spellcaster could rely on that to bypass super high AC with touch attacks? What if shooting someone with an arrow was a Target DC? This would make Attack AC and Target DC an opportunity cost, which creates fun and interesting player choices. Then we add more dynamics of saving throws and create an interesting flow chart of what a player wants to specialize into and what their character class / trope is capable of. Paladins could have an incredibly high AC and great Spell Save, but very terrible Target DC.

Critical Strikes with low dice

I also had an interesting thought, what if weapons always hit against AC if they rolled the maximum attack roll? That would make d4 weapons very sexy, but they'd have terrible damage (probably a d4). So let's say in order to score a critical strike you need to roll the maximum attack roll twice. Suddenly it feels really good to play a dagger because your chance of a critical strike is (25 / 25) 12.5%. This would make the dagger damage an average of 3.125 almost each turn (depending on how many attacks you get), which is just a little under the average of a d6. So maybe if you critical with a dagger it does more damage.

 

Then for big swords, like a greatsword with a d12, would be 8.3% (1 / 12), or (8.3% / 2) 4.12% chance to critical. What if a weapon had two dice rolls, like a maul had 2d6? Your hit average would be higher and your critical strike chance would be marginally lower (16% / 4) 4%. Though marginally lower, getting a critical strike with either weapon is substantially lower than a dagger.

Reverse Desire

For the moment I'm going to call a system that requires rolling the lowest number for the best result as Reverse Desire. Let's take all our examples and put it to the test here.

Light AC

Light AC is 4. Someone needs to roll a 4 or lower in order to hit us. For the lower end of the spectrum (4 AC versus d4 attack rolls) this doesn't change, but it changes significantly the higher we go. For a d6 weapon this would be a (16% * 4) 64% chance to hit. For a greatsword that would be (4 * 8%) 32 chance? Hmmm, that's worse than a d6. What if it was instead your weapon attack roll - the target's AC? So 12 - 4 = 8. This is a 64% chance to hit. Much better. But what about a d6? 6-4 = 2. 32%! That's also better! But is it easier? It's more crunch, after all. If our target audience doesn't mind some crunch then this is okay. It would be easy for a DM to determine if it hits: Just subtract the roll from the AC - if it's greater than 1 then its a hit!

Going with the theme of rolling the highest number is always a hit, what if rolling a 1 always hits? This would still allow daggers to critically strike.

Target AC would remain the same, essentially. Your Target Attack Roll could be a d10 versus someone in heavy armor with an AC of 12 but a Target AC of 4 would be extremely easy to succeed.

What else?

It almost seems flawed that a dagger could always hit someone, but let's also consider that we want a better game feel rather than emulating real life perfectly. With a lower hit die we will hit almost everything each and every turn, and with a bonus to our critical we can match the average damage of other weapons. Absolutely incredible. But also a dagger could never live up to the damage potential of a greatsword. (From my glossary: damage potential is the maximum damage roll you could make with one attack without adding additional damage from other sources.) The damage potential of a greatsword will always be ludicrously higher than a dagger (3 times as much, in fact).

Conclusion

I feel both systems have an advantage and a disadvantage. One involves more crunch than the other but offers an interesting game feel that should be explored. I'd like to explore both and make something fun out of it using a one-page game.