WOUNDS I: How many HP?

How many HP should something have?

WHAT SHOULD IT BE?

Well, I think, sticking with our rule of 7, a player should be able to be attacked 5-9 times before they go down, depending on class/role (tanks take more hits than glass cannons). Sticking with our rule of 3, most monsters should go down in 3 good hits.

HOW DOES OD&D PERFORM?

Going with OD&D guidelines, PC damage output is either 3.5 per hit (1d6) or 4.5 per hit (2d6, retain the highest) for your large weapons.

Most monsters do normal weapon damage too (1d6). Ogres deal 1d6+2. The larger giants deal 2d6+1, 2d6+2, and 3d6 damage. Sea Monsters deal 3d6 or 4d6. An earth elemental does 2d6-3d6. For "large animals" (including T-Rex!) damage guidelines are 2d6-4d6.

Thus, there's a rough pattern for monsters: They deal about 1d6 of damage for every 4 HD ("Tier"). So, a low level critter deals 1d6; a mid level critter 2d6; a high level critter 3d6; and the top of the scale is 4d6.

A 1+1 HD monster (say, a humanoid of some sort) vs. AC 3 (our fighter in plate) hits on a 15 (so 30% of the time) and deals 3.5 damage. The fighter likely has 4.5 HP. So, it will take about four rounds for a hobgoblin to kill a fighter. As soon as our fighter moves into the middle of that lower tier of play (level 2-3), it will take 8-12 rounds to kill him as he has gained extra HP. Then, he'll start facing mid-tier monsters and the cycle begins again, reducing surviveability again.

Our hobgoblin is AC 5 with 1 full HD. So, our first tier fighter needs a 14 to hit (35%). he deals about 3.5 damage, so he can expect to drop the hobgoblin about 3 rounds of attacking.

So, as we can see, OD&D fits my expectation pretty well, at least at low levels.

However, one thing that is likely frustrating is the low chances to hit. Each hit does a lot of damage but is unlikely to connect; i.e., the fighter is likely to miss twice and then splatter the hobgoblin with his third strike. My suggested to-hit system tends to give 50-66% odds of hitting rather than OD&D's 33% chance to hit. Thus, HP inflation needs to occur.

The Way Ahead

I want monsters to continue to largely use D6s for damage. So, we can tentatively go with 1d6/tier, with high damage monsters either getting a +1 or +2 bonus (or rolling 1d8 or 1d10). A typical monster will have 33%-50% to hit a plate clad fighter, so if we want that character to last for 7+/-2 attacks, then the character needs to have at least 10 HP. Against a middle of the road character (say, one in chain), the character would need ~14 HP to last for 7 attacks.

On one hand, I like the idea of players dealing 1d6 for damage. However, that really limits your possible weapons options and everything feels very much the same. It also likely undervalues two-handed weapons by giving them only +1 damage, basically. With D6s, your basic options for average damage output are:

1d6 = 3.5
2d6 retain the highest = 4.5, low results unlikely
2d6 retain the lowest = 2.5, high results unlikely
2d6 total both = 7

This is compared to my damage table (see another post) which tends to give results like:
1d4 = 2.5
1d6 = 3.5
1d10 = 5.5

In either event, though, the center of the road is 3.5. So for a monster to go down in 3 hits, it needs to have about 10 HP. It will take about 5-6 rounds to drop it. If that monster has a -1 AC penalty (that's -1 on a D6...), say, for being a "brute" then to stay up for 5-6 rounds it needs to have around 13-14 HP.

So we derive for monsters (for tier 1 at least):
Average monsters should have about 10 HP.
"Brutes" with -1 AC should get 13 or 14 HP.
"Soldiers" with +1 AC could get by with 7 HP.

And for PCs:
Weak/Light (leather, can take 5 attacks): 11.6 HP
Weak/Mod (chain, 5 attacks): 8.75 HP
Weak/Hvy (plate, 5 attacks): 5.8 HP
Mod/Light (leather, 7 attacks): 16.3 HP
Mod/Mod (chain mail, 7 attacks): 12.25 HP
Mod/Hvy (plate, 7 attacks): 8.2 HP
Tough/Light (leather, 9 attacks): 21 HP
Tough/Mod (chain, 9 attacks): 15.75 HP
Tough/Hvy (plate/9 attacks): 10.5 HP

The absolute high end of reasonable character archetypes would be 21 HP -- the barbarian with light armor and high durability. The absolute low end of reasonable archetypes is 8.2 HP -- the cleric in plate mail. The best range is likely within that -- I'm guessing somewhere from 10-16 HP.

Relating that back to mechanics I already have, what about 4+/-MOD (giving 1-7) + Max of Traditional Hit Die (so 4 for wizards, 6 for thieves, 8 for clerics, 10 for fighters)?

Or you can just give HP equal to the character's starting CON score. That is more luck dependent.

ADDENDUM

Dan over at Geek Grab Bag suggests that the worst case beatdown should have a defined Start, Middle, and End. That is, the overeager scout/thief that gets jumped while scouting should have about 3 rounds of survival, as should the mage that gets swarmed.

With hexes the most foes that can get in is 6. With squares its 9. However, at some point, most critters get large, so that limits the reasonable number of foes to 4-6.

4-6 monsters * 0.66666 to hit = 2.6666 - 4 hits per round. if you give a 50% to hit (...might be a good time to go total defense) its 4-6 * 0.5 = 2-3 hits per round. In OD&D (where monsters do 1d6 per tier), that'd be 9 - 14 HP (scenario A) or 7-11 HP (scenario B) each round. So your mage or over-eager scout needs a minimum of 21 HP to have a defined start, middle, and end to his Monster Mash experience.

You can get away with fewer HP if you allow for a Panic Button. For example, a limited healing power might buy you a round of time. So I'd say that maybe 14 HP is the minimum, and figure that the PC can buy themselves a third round either by killing off some of the bad guys mobbing them or use of a limited resource (consumable/power).

DOUBLE ADDENDUM:

Note that increasing monster HP with level requires increasing damage output with level too. Some ways that has been done:
- AD&D's ranger bonus damage
- Bonus damage vs. large critters (large critters tend to have more HD -- note that this nicely puts the game in two scales, so a fighter with a long sword can face a bunch of orcs and its interesting, or a bunch of ogres and its interesting; this is basically a fighter-only feature because its the bladed weapons that tend to do so much better)
- Multiple attacks for fighter types
- Magical "pluses" adding to damage rolls
- Chances to hit increase very fast (remember that fighter-type in "Against the Giants" that hit on a 2?)
- Spells that scale with level (the classic 1d6 per level for fireballs et al...)
- Scaling backstab damage (double, then triple, then quadruple, etc)
- Increasing critical damage (a 4E technique)
- Giving everyone double damage at epic levels (another 4E technique)

If you significantly scale monster HP with level then you MUST include some of these "work arounds" for players to keep pace.