D&D without To-Hit Rolls, Addendum

 I wrote this in response to LS's comment [1], but it ended up being super long!

Hope y'all find it useful still. :)

Hi, thank you so much for your reply!! So I’ve actually gotten some ire from damage-roll-only folks for the opposite issue, that the subtractive armor here causes attacks to miss too much. As much as I’d like to be an enlightened centrist and say that, if both sides are attacking me, then I must be doing something right, it’s entirely possible that I’ve really picked the worst parts of both methods.

You might know this already, but I had actually been pretty apprehensive towards damage-only combat rules for a while for the same reason! I don’t like HP bloat and I appreciate that armor makes opponents harder to defeat without just upping how many numbers you need to make to make their numbers go down. It was only because I’ve been exploring jrpg-style mechanics for my project (emulating Pokemon, Megaten, etc.) that I began considering one-hit combat at all!

So, part of the difficulty is that I don’t plan on having usual D&D combat, instead having a system where a starting character with ~10 HP can always deal ~4 damage, and mook monsters will have only between 2 and 6 HP. I talk about this in the motivation section, but really my goal with this was to see whether doubling HP across the board would be intuitive and not statistically annoying (a function of HD depletion rate).

One solution to avoid bloat is to let each HD be 6 HP, which is just below the virtual HP per HD of D&D! This means that each hit has a 1/6 chance of depleting a hit die, but it also means that wearing armor always guarantees you at least one more hit before dying (since it is not possible to roll even 1-6 minus 1 and exceed 6). However, this is true for 4-out-of-6 HD rolls above anyway; one-hit-depletion here is only possible by virtue of low HD rolls of 2 × {1, 2, 3}.

Letting each HD be 4 HP gives each one a 50% chance of depletion without armor. This sounds similar to how typical D&D turns out, but yet it is variation in HP and damage that ensures hits won’t always be depleting ones. On that note, though, it is also an approximation of using my method without doubling HP! So if you wanted to get rid of to-hit rolls without doubling HP, you could just do that! It would only be literally twice as lethal, which might not be a bad thing.

It's here that I want to shout-out Errant for, when converting old-style monsters, having a base of HD = 5 HP. It's modified there by adding HP for increased armor (the actual formula is taking a monster's ascending AC and dividing by 2). However, if you treat armor as subtractive from damage rolls rather than additive one-time to HP, you could just leave each HD at 5 HP. Combat would become slightly more difficult because armor that inhibits damage, whether by being subtractive or via to-hit rolls, results in virtual HP that is not ever actually lost. Errant's solution, then, is simpler and less annoying in terms of attacks failing, but it requires stat conversion overhead and tracking more HP than just letting HP = 5 HD [2].

In any case, my benchmark is always an HD 12 gold dragon which in OD&D has an  average of 42 HP or a maximum of 72 HP. Doubling these results in 84 and 144 HP. Letting HP = 6HD results in 72 HP always, and HP = 4HD results in 48 HP always [2]. The original method, the double HP method, and the HP = 6HD method are roughly equivalent with respect to how many rounds it takes to deplete an HD, but the last method simulates well the expectation that a successful round of combat should necessarily result in HD depletion. I think double HP or letting HP = 6HD would be the least frustrating in terms of vulnerability, but letting HP = 4HD or just keeping normal HP keeps math low at the expense of (without to-hit rolls) double vulnerability.

Sorry for the extra mathematical explanations on everything, but I hope this is helpful just to figure out where my method came out of, how you could remove TH rolls without bloating HP as much, and what the trade-offs of each method are :)

 

[1] Comment on original post: https://traversefantasy.blogspot.com/2022/03/d-without-to-hit-rolls.html#comments

[2] Errant also has characters hitting for more damage than just 1-6 more frequently, with abilities and magic weapons etc. This means it takes a bit more math to figure out than just talking about it in terms of a 1-6 roll depleting an HD-equivalent!

[3] For extra credit: a red dragon in Errant has 100 HP (20 AC / 2 * 10 HD). If we were just going by HP = 5 HD, though, it would have 50 HP. On average, a red dragon has 35 HP in OD&D and 45 HP in B/X, since the two use 1-6 versus 1-8 for HD respectively.