Old-School Reduction: Attacks, Hit Dice, and Saving Throws

This is part of a series describing my efforts to apply reductionism to OSE. My aim is to boil down some of the basic rules to something that can be easily transplanted into other systems. Much inspiration for this effort comes from the 1974 Style ruleset (itself inspired by Searchers of the Unknown), but I want to take things even further.

Last time I defined a baseline set of key stats for human characters and a somewhat different take on how ability scores modify them. Okay, fine… but how does this all actually work in practice? I'll take a "bottom up" approach to answering that.

Attack rolls

Target 20 helped me to stop worrying and learn to love descending AC. Even so, the attack roll needs to be as frictionless as possible. Here's my take.

1. Roll 1d20.
• 20 always hits.
• 1 always misses.
• Otherwise, follow the remaining steps.
2. Add the defender's AC to the roll.
• Ignore AC adjustment due to shield if the defender is fleeing from melee.
3. Add modifiers to the roll as determined by the ref. Some examples:
• +2 if the defender is fleeing from melee.
• +1 if the defender is within optimal (i.e., short) range for a missile weapon.
• -1 if it is within 2-3× optimal (i.e., long) range for a missile weapon.
• -1 to -4 if the defender has partial cover.
4. If the result is greater than or equal to the attacker's TH, the attack hits; otherwise it misses.

This is mathematically identical to the OSE and Target 20 procedures—unless I've miscalculated—but using THAC0 directly as the target value feels more streamlined to me. There's plenty of room here to "plug in" extra rules, such as fumbles, critical hits, manoeuvres, and so forth, if desired.

Hits and hit points

Rather than rolling for damage, each attack delivers a certain number of "hit points" (hp) determined by the weapon used. (Again, yes, I have repurposed that term.)

Type	Damage	Examples
Improvised	1hp	sharp stick, applied fists and boots
Light	2hp	club, dagger, sling, staff
Medium	3hp	axe, bow, mace, short sword, spear
Heavy	4hp	battle axe, long sword
Very heavy	5hp	pole arm, two-handed sword

With the exception of crossbows and similar devices, hit points for a successful attack are usually limited by the attacker's AT, which is itself modified by the Strength ability score. In other words, an adventurer with AT3 deals at most 3hp per successful attack, even if they use a heavy weapon, but only 2hp if they use a light weapon. However, I'd likely rule that a critical hit (i.e., unmodified 20 on attack roll) delivers the highest of AT or the weapon's damage rating, if not more.

[EDIT: I have long since changed my mind and gone with a flat number of hit points based on AT, with the exceptions of unarmed attacks inflicting AT-1 (to a minimum of 0) and devices like crossbows inflicting a fixed amount.]

For monsters, AT is the average of the listed damage roll rounded down, to a minimum of 1hp. For example, a boar deals 5hp (AT5) for its 2d4 tusk attack. Where a creature has multiple attacks, they are separated with commas. For example, a grizzly bear has AT2,2,4 for its two 1d4 claw and one 1d8 bite attacks. Alternate attack routines are separated by semicolons. For example, a white ape has AT2,2;3 for its two 1d4 claw attacks or one 1d6 thrown rock.

Again, lots of room here for additional rules. This just seems to me like the simplest starting point.

Hit dice

When a creature suffers harm, use the following procedure to determine if it survives. (Recall that the notation for HD is x+y.)

1. Keep a running total of all hit points sustained up to now—tally marks should do.
• If the total is less than x+y, skip the remaining steps: the creature is basically unharmed.
• If the total is 6x+y or more. skip the remaining steps: it's dead, Jim.
2. Roll a number of d6s equal to x.
3. Sum the values and add the y modifier.
4. If the result is greater than the running total, the creature absorbs the hit and continues to function; otherwise, it's out of action and—depending on your preferences—probably dead.

This is obviously different from the way "hit points" traditionally work, but it's functionally the same, more or less. The "drama" of rolling for damage is replaced by the "drama" of rolling hit dice to see if the damage was absorbed. One of my key objectives is to minimise erasing, so we're making tally marks and clearing them only as the damage is healed (1-3hp per day of complete rest) instead of repeatedly smudging out and rewriting a number.

And, yes, the basic idea was shamelessly stolen from DURF.

Two questions I find interesting about this approach that I might explore later.

• Should something special happen if the result of rolling the hit dice exactly equals the running total of hit points sustained?
• Should it be possible for a 0hp attack to force a re-roll of the hit dice?

Each OSE character class has its own particular size of hit die, but I can't decide whether I want to incorporate this level of detail or not. I might come back to it another time.

Saving throws

When things go terribly, terribly wrong, a creature must make a saving throw to avoid (or at least reduce) the effects, which are otherwise often fatal. The procedure is straightforward.

1. Roll 1d20.
2. Add modifiers to the roll as determined by the ref. For example:
• +4 versus poison or similar death-dealing effect (D).
• +3 versus aimed effect (W).
• +2 versus paralysing effect (P).
• +1 versus area effect (B).
3. If the result is greater than or equal to the creature's SV, the effects are avoided or mitigated somehow; otherwise, they suffer the full effects.

The main difference here is the single target value, which is the highest of the five OSE saves (typically S). Again, this is for the sake of simplicity. If different modifiers based on character class seem important, they should be relatively easy to reintroduce.

The story so far…

I've covered the use of the AC, HD, AT, TH, and SV stats. That still leaves MV and ML, but those are best considered in the context of a combat round, which I'll explore next time.