“Quick, we must retreat!”
“Why? You look absolutely fine to me.”
“Yes, but the next the next sword blow will surely kill me.”
“Have no fear, I will leap into the fray and hold them off, for I am fresh, so even if they all strike me I shall remain standing.”
Such are the caricatures of the abstraction of HP; combatants can take HP ‘damage’ without risk until they’re right down to the little numbers. These caricatures, and the implicit criticism, have some merit. Players do know that the Orc with a handaxe (1d6 damage) will not be able to kill their 8HP Fighter on this round. And they do know that their 6th Level Fighter, whittled down to 3HP, is now in serious trouble, even if we can see no difference in his physical capabilities.
Or rather, we think we can see no difference in his physical capabilities. The 5e Basic pdf says "The loss of hit points has no effect on a creature's capabilities until the creature drops to 0 hit points" (v0.2 p75). Of course I know why the rule book says this: we don't apply penalties to characters and creatures that have taken HP damage. But it is language like hinders and 'proper' understanding of the abstraction of HP and D&D combat - though as I note below the abstraction of HP is terminally undermined in newer editions. When the abstraction is understood, we can see that of course a loss of hit points does have an effect on a character or creature's capabilities. A PC with 3HP has far less ‘fighting ability’ than one with 30HP, even if their AC and THAC0 or BAB remain unchanged. Simply put, the 3HP Fighter will survive fewer rounds of combat than the 30HP.
But anyway, it is often difficult to grasp such abstraction, and the 'certainties' (see above) that it produces can sit uneasily with players and DMs. We might intellectually understand the abstract nature of D&D combat, but we often - instinctively - fall into making sense of these numbers (HD, HP, AC, ‘to hit’ rolls, etc.) as if they had a one-to-one correspondence with world.
So, let’s make things a little more uncertain, shall we?
Carcosa has PCs roll their HP at every encounter. You also have to roll to see what type of HD you have! Fun for a diversion, but the certainties in the two 'examples' above are not mitigated. Why not have the PCs roll their HD every time they are 'hit'?
Here’s how it would work:
Characters and creatures start with 0 'hit points' (HP). They have not yet been 'hit'. When a character or creature is 'hit', damage is rolled as normal, and this many hit points are added to their HP, which accumulate. A character or creature rolls their HD every time it adds points to their HP. So that 6th Level Fighter would roll 6d8 (assuming no modifiers from CON), giving him somewhere between 6 and 48HP. It wouldn’t be quite as 'swingy' as that might look as the multiple dice produce a pronounced bell curve. If the total rolled is greater than the accumulated HP of damage, the character or creature can fight on. If the number roll is equal to or less than the accumulated HP, the character or creature is either dead or has suffered a serious wound.
Naturally, I need a good critical hit chart to generate the wounds and determine the chance of death. I am tempted by the extended critical hit charts from WHRP1e (found in the Character Pack, maybe one of the Apocrypha books) which have different charts for all kinds of weapons and sources of damage. ACKS’ ‘mortal wounds’ table might also be a suitable base. While I would want the procedure to be relatively simple, I'd also have to work out a simple set of modifiers to rolls on this chart. Presumably these would involve level, CON modifier, and perhaps the difference between accumulated HP and the last rolled HD total. And death? This would either be an automatic result on the far reaches of the chart, a consequence of a wound that is not treated or bound in time, or perhaps, to keep things simple, a Saving Throw (vs Death). For simplicities sake, most monsters and NPCs might die as soon as the HD roll is not greater than accumulated HP - this is a system about PCs, after all.
Or maybe the 'dice-drop' table I suggested ages ago...
Whatever table I eventually use I've a feeling that it will have to be kind to the PCs. Or, at least, as kind as a critical hit/serious wound table can be. PCs are going to be more vulnerable using these rules. While 1st Level PCs will get killed/wounded by a single blow in this system and the traditional one, the real effect will be on PCs with around 3 or 4 HD. In the traditional system there is no chance that the first sword blow will drop them (especially with the kind of house rules that boost HP - max HP at 1st Level, re-rolling 1s, re-rolling all dice at each level, etc.), in this system some of those formerly 'insulated' PCs are going to fall in the first round of combat. But then, so are some of the monsters in the same HD range, which brings a much wider range of the bestiary into play much earlier on... along with larger treasures and greater XP rewards. Swings and roundabouts, eh?
But why do this?
Well, it gives me an excuse to use a critical hit chart. And do I love me a good critical hit chart. But it also means that even PCs (and monsters) of moderate to high level/HD are in an uncertain amount of danger once the daggers, axes, and swords are drawn. The cartoon criticism of D&D's accumulating HP is disarmed. Sure, higher level characters are far more likely to be able to fight for longer than low or zero level characters, but there will rarely be the guarantee that the next swipe of a sword will not do for them.
But more importantly than that, much more, it allows me to incorporate an aspect of ‘newer’ D&Ds from which I have always recoiled – easy HP recovery (or easy HP reduction, given what HP 'mean' in this system). As I've said, the abstraction of HP and D&D combat is often difficult to maintain in the imaginations of the DM and players. And players and DMs really do need to buy the abstract nature of HP and D&D combat in order to understand how the game effect of low HP = reduced overall fighting ability = a ‘wounded’ state. But for this abstraction to work, HP ‘healing’ has to be slow and/or difficult. If a PC can easily replenish their all HP, say with a ‘long rest’, the HP abstraction is terminally undermined. If a good night's sleep allows a PC to recover all their lost HP, then low HP very definitely does not = wounded, not even as an abstraction.
But at the same time I will concede that rapid HP recovery can improve some aspects of the experience of play. If PCs can recover their HP by taking a rest, swigging some brandy (see Crypts & Things), or hearing a rousing speech, then (of course) they can get a lot more adventuring done, especially during the first few levels of play. And these early levels are the key to a sustained campaign. So I'll be experimenting with this system in the next games that I run.
As a final point, easy HP recovery and no ‘real’ wounds means that PCs can fight all day, every day. This puts them on the 5e track – which given the 'XP per adventuring day per level' table in the DMG pdf I can safely caricature this as 'How to Hit Name Level in 30 Days, or Your Money Back!' I know that this meant to make players feel 'epic', but I can't imagine feeling less 'epic' than having my character, starting at 1st Level, is set to become a mighty lord in a matter of mere weeks of game time.