D&D Thinkpiece: Hit Dice

    Since everyone and his uncle has an opinion on Dungeons and Dragons, I thought, "Why not me?"  (This may or may not be a new series; we'll see how much energy it takes.)  Today, we'll be looking at hit dice.

    Hit dice are something that have bothered me since I started looking at 3.5's simulationist tendencies.  Hit points, since first edition, have been a combination of toughness, luck, skill, and divine intervention; hit points, as they say, represent hit points.  But hit dice have always scaled with creature size—yet never in a consistent way.

    What if (racial/monster) hit dice really were an abstraction of physical mass?  If a human is a 1d8 creature, let's say 1d8 is equivalent to about 200 lbs (sorry, metric friends).  That would make 1d4 equivalent to 100 lbs, 1d2 equivalent to 50 lbs, and 1d1 equivalent to 25 lbs.  More massive creatures get additional d8s added—2d8, 3d8, etc.  Doing some quick math, the average weight for a common dolphin is 180 to 330 lbs, equivalent to 1 or 2 HD.  The average weight for a black rhinoceros is 2,425 lbs, or 12 HD.  And the average weight for a camel is about 1,000 lbs, or 5 HD.  That doesn't seem so bad.

    Polar bears are about 4 HD, lions about 2 HD, and Komodo dragons about 1 HD.  Bison are 8 HD, saltwater crocodiles 11 HD, and leatherback turtles 4 HD.  Mid-sized creatures don't seem terribly over- or underpowered in this system.  But what about the extremes?

    It turns out that none of the classic familiars can be modeled this way; only the fattest of housecats reaches 25 lbs, and D&D doesn't function on a scale smaller than 1d1.  Birds are also an issue, due to their hollow bones and correspondingly lower mass: mute swans, Andean condors, and Haast's eagles all cap out at around 25 lbs, or 1/8 HD.  Arthropods have the same problem; griffenflies, a group of prehistoric dragonfly relatives with a 3-foot wingspan, don't even rate!  And garden-variety tarantulas?  Forget about it.

    Modeling interactions with individual rabbits might be an exercise in futility anyway, at least for a game like D&D.  It would be easier to treat swarms of gnats as a hazard than a creature—25 lbs of gnats is too many gnats—and small animals are more likely to flee or hide than interact with human-sized things.  Such creatures should be left unmentioned, except as set dressing, or treated as an auto-kill with no XP value.  Maybe vertebrate swarms, like rats, can be left as-is; I can imagine 25 lbs worth of rats.

    Okay, we've handwaved the problems with lightweight creatures; what about super-heavy creatures?  An African bush elephant averages 17,600 lbs or 88 HD.  An orca, at around 8,000 lbs, is equivalent to 40 HD.  Estimates for the largest tyrannosaurs are around 10,000 to 16,000 lbs or 50–80 HD.  That's... too much.  Especially since Reflex saves scale with hit dice!  Imagine a humpback whale with 300-odd hit dice; even with a Dexterity of 1 and poor Reflex, that thing is going to make every save you throw at it.  I suppose you could deny them Reflex saves and treat them as living siege engines, but then you would need some sort of siege engine combat sub-system...

    All right, clearly there are some issues with the idea.  However, it would provide a real-world model for an in-game stat (something 3.x gestures at more often than other editions), as well as allowing hit dice to scale consistently.  It doesn't help with class-based hit dice, but those have always been tracked separately from racial hit dice; dragons with class levels are a great example of that. There is still the problem of spell and weapon damage, which might have to be adjusted at higher levels to account for 30-HD aboleths.  Furthermore, creatures like fey and dragons, which in 3.x have non-d8 hit dice, would need to be modified and might end up wonky for monsters of their CR.

    Ultimately, most people willing to do the work of overhauling the Monster Manual already have their own houserules to make things simpler, or more realistic, or what have you, so this is more of a thought exercise than a recommendation.  Lacking a playtest group of my own, I'm sadly unable to experiment with this sort of thing in the wild.  Do the fights slog on at higher levels?  (Yes, always.)  Is killing wall geckos an integral part of the D&D experience?  (Probably not.)  If anyone does try out combat using this system, please let me know how it works!