Monday, September 08, 2014

Stamina, Hit Points and Pain

Had a great conversation with +Douglas Cole last week regarding hit points, damage and luck. He wrote a very interesting article on separating luck (karma) from bulk hit points.

Now parting from the premise that luck and hit points are two different values I'd like to develop the idea further and in turn break hit points into two values: stamina and hit points proper. The purpose of this is to build a system around these two values that grants the skilled fighter a fighting chance by not allowing a quick death, but at the same time granting the skilled fighter and the thoughtful player a quick kill in an encounter.

The hit point mechanism I'm currently using in Saints & Sinners allows for low damage weapons to take a long time to defeat the enemy while high damage weapons will neutralize the enemy quickly, possibly in the first hit. On reading this you might say, well duh! That's always been the case. Well no if we consider what low damage and high damage is and how long I'd like to fighter to last. Let us consider low damage as something that goes  from 1 to 4 hp, medium from 5 to 10 hp and high from 11 to 18 hp. I'd like a combatant taking 1 to 4 hp per hit to require 15 to 20 successful hits (not rounds) to die. The same character suffering medium damage per hit (5 to 10 hp) should last 5 to 10 hits and at the same time a high damage hit should neutralize the character after one or two such hits. This corresponds respectively to : a fist fight, a knife or sword fight, and a .45 to the chest area.

The problem here is this design requires a character to perish when he suffers 18 hp ( a single high 18 hp hit), when he suffers 32 hp (6 medium 6hp hits) and also perish when he suffers 60 hp (20 low 3hp hits). Since I'm talking about hits and not rounds or attacks, elements such as: armor, skill and luck don't play a role. I already know the character has been hit.

Without further delay here's the mechanism and how it's worked for me. First of all some definitions: stamina is the body's capacity to endure damage while hit points are the sheer life force of the character or creature. A character dies when hit points reach zero regardless of stamina value.

To make this work I'm going to do here is take a bit of stamina and call it pain threshold. This will act as a window or per-hit buffer that will allow damage to be channeled either to stamina, hp or both. The result is a damage transfer as shown in the following graph which shows damage to hp and stamina based on the per-hit damage delivered to the character. Any value below or equal to the pain threshold is dealt to stamina only. Any amount that overflows is delivered to hit points. So a character with 32 stamina points, a pain threshold of 4 and 18 hp would be represented as follows. The yellow line represents the relative damage being dealt by the blow.

Anything less than or equal to 4 causes no damage and is absorbed by stamina (the blue line). Once damage reaches 5 points it begins to overflow to hit points and stamina is unable to absorb any more damage (blue line levels out for any further damage). The character becomes vulnerable at this point as shown by the rising yellow line. Initially the line is around 3 (30%), representing small wounds. It then increases to about 6 (60%) representing serious wounds. At 23 points delivered per hit the character dies in a single attack. This is due to the fact that 23 points - 4 stamina (pain threshold) is 19, and that's one point above the character's 18 hp.

Modeling this the system performs as the following graphs show. Each graph has a blue line representing damage delivered per hit. This is a random value between the specified ranges: 1 to 4hp for low damage, 5 to 10hp for medium damage and 11 to 18hp for high damage.

The orange line shows initial stamina value and how it decays over time. The yellow line shows hit points and its decay over time.

When suffering low damage  (1 to 4 hp per hit) the character's stamina is very effective. Hit points don't begin to drop until the character runs out of stamina. This happens around hit 9 and 10. The character finally perishes at hit 18.

When suffering medium damage (5 to 10 hp per hit) the character's stamina and hit points drop alongside each other. With every hit the character's stamina is able to stop part of the damage, but not all. The character perishes at hit 6.

When suffering high damage (10 to 18 hp per hit) the character's stamina is not very effective. In this case it stops enough to prevent the character form dying after the first hit, but the second hit is a game stopper for the player. The character perishes after the second hit even when the character still has two thirds of the stamina points left.

This mechanism has worked really well for me in putting tactics in the forefront of an encounter. A quick entry into a room, a backstab, sword fights and a fist fights now fit better into place without compromising those lengthy fights we enjoy in our games nor placing our characters in the extreme danger of a highly lethal game.

Here's a quick houserule you might want to try out in D&D like games.
HP = CON + level 1 hp roll
Stamina = CON + level 1 hp roll
Pain threshold = Stamina * CON / 100, rounded up to the next integer. Example 1.1 rounds up to 2.

All future hp increase due to leveling is added to stamina, not hp. After each roll the pain threshold is recalculated. Hit points stay fixed forever, representing the underlying fragility of the character. Stamina on the other hand represents the battle hardened character. As stamina increases so does the pain threshold and the less likely the character to suffer damage to the vital hit points.

This rule will be better applied to OSR like games with low hit point damage weapons than the newer high-damage-feat-powered attacks.

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