How does it affect the game if PCs have lower maximum HP?

Question

The book uses Constitution score, not modifier for determining maximum HP:

Your maximum HP is equal to your class's base HP + Constitution score. You start with your maximum HP.

Maximum HP is quite high for player characters — usually it's 15-20, while the possible maximum is 26 (minimum is 12). For comparison, typical monsters have 6-8 HP, solitary dangerous ones has 12-14, and a dragon has 16. Considering healing magic, it becomes really hard to die exclusively from the HP loss in one fight.

I've seen a game once when the GM messed up and uses the modifier instead. Surprisingly, the game was fun and exciting — having less hit points encouraged players to be less reckless, to prepare better, to care about each other's health and search for more tactical approach in fights. That makes me wonder if this was a horrible mistake or a brave idea. Now I'm thinking about getting such an experience in my own game.

As a GM, what changes should I expect starting the game with less maximum HP for player characters?

Or is it really a bad idea that shouldn't really work?

Answer 1

Unless you revise damage and/or healing, this will take "deal damage" out of your toolbox as a GM quicker than you'd want.

Apocalypse World introduces the "harm move" as a way of imposing unpredictable consequences when a PC suffers any harm at all. In Dungeon World, the unpredictability is the damage roll - everything can basically do up to twice its average damage.

If you just base HP off of Con modifier, then a reference Wizzrobe, with 9 Constitution and no armor (and therefore 4 HP) has a chance to die any time they take damage from anything at all, meaning you can only throw "deal damage" at Wizzrobe if you intend for them to die and be gone forever. Even a rather sturdy Wizzrobe, with 13 Constitution and some simple armor (5 HP 1 Armor), can still die from 1d6 damage, which is, like, "pathetic goblin spear" levels of damage.

"Deal damage" is both "use up their resources" (the healing items) and "offer an opportunity that suits a class's abilities" (any class with a healing move), but it's only those things as long as you can be sure that whoever you point it at isn't going to die. And it's pretty much always there as an option for when the GM is looking for a move to make - the adventurers just need to be in a position where it makes sense they risk getting hurt, which is pretty much the default state of adventurers.

Unless you revise damage to be more consistent or healing to be able to pull people back from the brink, such that you can deal damage to someone and be confident they won't die, this HP change will not only make PCs who are supposed to be armored and tough much more vulnerable, it will make PCs who are supposed to be vulnerable die, sometimes, in a single hit. And so you can only point that single hit at them, as a GM, if you intend that they should die.

Answer 2

Defenses

A glaring omission from your original question is armor. One of the several reasons the 16HP dragon is so much more difficult than the other monsters is its whopping 5 armor. If your average Hunter or Soldier gets lucky enough to land a hit, there is a 1 in 6 chance the hit will do any damage at all (and incidentally, roughly a None in Hell chance he'll survive the following four seconds. The best defense is a massively overwhelming offense). A well coordinated group might be able to improve on this by triggering the Damage From Multiple Creatures rules (page 22) for +1 per creature after the first, but good luck keeping them that coordinated.

Yes, it's possible for a PC to have more HP than a dragon. But unless you're talking about taking a single massive hit (or some weapons with the Ignores Armor tag), the huge armor on a dragon will more than even things out.

Damage

How much damage the players take depends almost entirely on the GM's choices. When the GM gets to make a move, there are twelve default options, and only one of them is Deal Damage. That damage isn't even necessarily to a player character, and damage is often the least interesting thing that can happen. Only the last hit point really matters; any other hit point loss is just increasing the dramatic tension around the possibility of losing the last one.

Anecdotally, I once ran a two-session game in which the PCs collectively took damage a grand total of once. It was an exciting game full of action and adventure because the characters were doing exciting things, making difficult choices, and discovering interesting things about each other and the world.

General GMing advice is if you can't accept any outcome the dice may show, then don't roll the dice. You know how much HP the player has, and how much damage a hit could do. If you're not comfortable with that (and you can avoid it), simply review the list of moves and pick something else. In many cases, it can be as simple as giving the player another chance to avoid the damage by prompting them toward a defy danger move. In other cases, you can simply choose put someone in a spot instead.

Denouement

This approach shouldn't play too much differently than skipping the story ahead to when the PCs had a hard fight to get where they are and everyone lost some HP. How risk-averse the group is is not up to the GM, but the GM can control how lethal he wants to be. In the end, the GM must follow the Principles and the Agenda. Filling their lives with adventure might mean trying to kill them, but it doesn't have to. If it doesn't make for a great story, then pick a different move.