I must create a system, or be enslaved by another man's. I will not reason and compare: my business is to create.

- William Blake

Sunday, May 19, 2019

Bounded accuracy in combat: OSR, D&D 5e and Dark Fantasy Basic

Warning: this post got very technical, very fast. Is mostly about number crunching through editions. Hope you enjoy it anyway.

So, D&D has this thing where your "to hit" bonus rises faster than your armor class AC. Soon enough, everybody is hitting everybody a lot more often.

On the other hand, hit points (HP) rise faster than your damage. So, while you're hitting more often, each hit takes a smaller percentage of your enemies HP.

These two thing balance of another, sort of. But there are also other things to consider. For example, Making numbers too high is usually a bad idea, because adding and subtracting all the time detracts from the flow of combat (this applies to "to-hit" and AC, but also HP and damage). Making numbers too small ruins granularity; a 10th level fighter (and, arguably, a thief) should hit more often than a 1st level one, but a 10th level wizard should (arguably) still have SOME chance to hit an opponent that is adequate to a 10th level fighter. Missing attacks often is boring; but if you hit all the time, you will probably deal less damage, and rolling attacks over and over again is equally boring. Etc.

There are numerable ways to deal with this.

In old school (and most OSR) games, the most usual method is keeping AC more or less stable, adding decent amounts of HP and to-hit bonuses, and SOME extra damage, but not much, unless you use weapon specialty rules. You may also get additional attacks, which raise damage per round.

In D&D 3e/4e, you get LOTS of bonuses. HP is significantly raised. To-hit bonuses rises faster and longer. Now AC is bigger, creating an arms-race of sorts. Damage gets bigger, but perhaps not always big enough. It is said that in 3e, creatures get so much HP that damage becomes less significant, although I don't have enough experience with the game to say for sure. In 4e and games like 13A, damage get exponentially bigger, like HP (although IIRC 4e had to be fixed because monsters just had too much HP).

D&D 5e tones things down a bit. To-hit and AC are diminished almost to OS levels (in fact, often even LOWER than OS levels), but damage and HP are closer to D&D 3e (without the 4e HP inflation). A wizard has a to-hit bonus that is not that far from a fighter, but the fighter gets extra attacks, the barbarian gets higher damage, etc.

Another interesting thing about 5e is that you're chances to hit an appropriate opponent are more or less equal at every level. Compare this to OS games where the chances to hit get higher and higher, but damage gets proportionally lower.

Let's do a quick and very rough comparison of a monsters in these systems (the stats are from S&W, Pathfinder, 4e and 5e).

Adult Red Dragon [OSR / 3e / 4e /5e]
Attack bonus (claw): 10/25/22/14
HP: 40/253/750/256
Damage (claw/bite): 23/40*/50*/55*
AC: 17/29/33/19
* Damage is WAY trickier. In 3e, the dragon can makes lots of attacks with tails, wings, etc, (apparently) at the same time, while in 4e it cannot "bite" and "claw" at the same time, so I've only counted claws. But it can also take reactions, free action, etc. 5e also has legendary actions every turn. So, hard to compare.

I'm not even sure the iconic red dragon is the best comparison, since modern editions (rightfully, IMO) made them more dangerous on purpose (in fact, the Rules cyclopedia already made them more dangerous in comparison to AD&D, for example). But it serves to illustrate the "number bloat" in comparison to earlier editions.

There is no right or wrong here; I dislike dealing with monsters with 750 HP or +25 to-hit, but they serve a function. For example, they make monsters more "epic". One hundred 1st level archers would stand little chance against this dragon in 3e and 4e, but they might win in 5e, and will destroy the dragon in AD&D or Basic D&D.

In my own game, Dark Fantasy Basic (DFB) - a mix of old school (specially Moldvay´s Basic) with modern stuff - I prefer to keep big numbers in check. The to-hit bonus are, at most, something close to +20 at the highest levels (that would be level 15th in my planned next iteration; currently it has only 10 levels) - suits a d20 roll very well, IMO.

Monster AC is unchanged from AC, but they get an HP boost. For PCs, they get a boost in both AC and HP. Damage is doubled for monsters, almost doubled for PCs.

I use this OSR to 5e conversion, BTW.

As you can see, DFB plays like an OS game in this regard - the higher your level, the most often your attacks land.

The difference between DFB and these other examples is how I closed the gap between high HP and more or less static damage. In DFB, whenever you hit a number that is equal to AC+10, you get a critical hit, which raises damage. So, not only you hit more often, but you also crit more often. AFAIK, Pathfinder 2 will use a similar formula, but there are certainly other examples outside of D&D.

This allowed me to make high-level combat somewhat shorter and still maintain an epic feel to big monsters (but probably not as much as 3e or 4e), while avoiding dealing with big numbers all the time.

Again, there is no right or wrong - it is mostly a matter of taste. If you would like to see how this turned out in my game, you can check Dark Fantasy Basic here.


  1. Landing attacks often is boring. What I like in OSR is that creatures often don't have that much hp, but can kill with one hit by poison or some other means. Like, roll save vs poison or die on the spot thing with giant centipede. There's a chance you will kill it with one hit, and vice versa. Pounding creatures with dozens attacks is plainly boring and removes satisfaction of victory for me.

    1. While I agree in general that a large number of blows is unsatisfying, the "once and done" is sometimes a bit rough to me. Granted, this in part may be from years of 3.5 D&D where the time sink in building characters can be hours. So while I don't lament a character's death, having to spend the hour(s) building a new character sucks.

      If I got back into the more OSR style, I may be swayed back to enjoying this style more.

    2. Kane, to each their own, but after the first few levels, killing creatures often take multiple blows in OSR too. 5e has fights that are supposed to last about three rounds; I would bet most OSR fights take longer. If landing often is boring, missing often can be even more so!
      Anyway, it as an interesting topic. I appreciate the idea of "killing with a single blow", but it goes against the whole point of having HP in the first place, so it should be balanced, IMO.

  2. I agree with Kane, the OSR relishes shorter, brutal battles. However, some greater monsters (like a dragon) should be tough enough to last 10 rounds... or kill the entire party.

    PC creation has to be cut down to 20 minutes or less, assuming the adventure is a meatgrinder. Who cares if you taught singing lessons to the prince's cousin when you're brawling with a tentacled scorpion?