Single roll combat (and more minimalist mass combat)

I nearly finished a document of about ten pages on mass combat in OSR systems. 

My idea, as I had already discussed a few times, was not to introduce a new/alternate system (Chainmail, Warmachine, etc.) new types of data, replace the d20 with a d6, or rewrite a troop list, but to simply to use the rules/stats as they are written in systems like B/X or AD&D, and extrapolate those rules to cover a much larger group of creatures at once, or to cover a longer period of time. In other words, to try to summarize several rolls into a single one.

I approached this issue through four paths: one versus one, which I thought could simply be ignored; one versus many, allowing powerful characters to attack many weak enemies at once; many versus one, which allows the opposite; and many versus many, which are rules for battles between groups of different sizes against each other.

In the end, I decided to add a small idea about how to resolve any combat with just a single roll. Ultimately, I am concerned that this idea may have made all my other ideas obsolete, since it solves almost any situation. The only caveat is that the combats must be between creatures of approximate power. If you avoid absurd situations like a thousand versus one, it should work in situations up to fifty versus twenty, one versus ten, and so on.

Here are some ideas that might give you the gist of it. And maybe this is already enough that the doc is not needed... But let me know if it sounds interesting.

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The margin of success

When you make an attack roll, subtract the target number from your result. That difference — positive or negative — is your margin, and it is added directly to damage on a hit. Optionally, a miss works the same way in reverse: a near-miss deals reduced damage rather than nothing, meaning every roll moves the fight forward.

A fighter needs a 10 to hit and rolls a 14. Margin: +4. His sword deals 1d8 — say he rolls a 5 — for a total of 9 damage. If he had rolled a 7 instead, missing by 3, the optional rule gives him 1d8 minus 3 — perhaps 2 damage — a glancing blow that still counts.

The group attack bonus

Ten bandits attacking a single knight roll once, with a +10 bonus, and deal one die of damage plus the margin. No rolling ten separate attacks. One roll, one result.

Conversely, the knight can attack all ten in a single attack with a -10 penalty. If he hits, he damages ALL ten bandits at once (10 is the hard limit; the knight cannot attack 100 at once).

The bandits need a 12 to hit the knight and roll a 9, adjusted to 19 with their +10 bonus. Margin: +7. They deal 1d8+7. The knight is not struck ten times; he is overwhelmed by a sustained press whose worst moment is captured in that single roll.

The knight strikes back. He needs an 8 to hit a bandit and rolls a 14, but with a -10 penalty that becomes a 4. A miss. The bandits' formation holds for now. Next round he rolls an 18, adjusted to 8. He hits, margin 0, deals 1d8 damage with his sword. If the bandits only had 4 HP each and he rolls 5 damage, he might have cut down all ten at once.

Groups of different sizes

When two groups of different sizes fight each other, the larger group gets a bonus and the smaller group gets a penalty, equal to the difference in size. Seven bandits against five knights: the bandits attack with +2, the knights with -2.

In some cases the groups can be reduced to a common denominator. Six bandits against four knights can be treated as three bandits against two knights, keeping the same proportions with fewer units to track. Twelve against eight becomes three against two. This is purely a matter of convenience — the math is identical either way.

The single roll method (optional)

Both sides roll one attack each, simultaneously. Apply the margin to average damage. Compare remaining HP. The side with more left wins; the loser drops to zero; the winner keeps only their remainder. Two rolls, a subtraction, a comparison, done.

Two ogres, 19 HP each, average damage 6, needing a 10 to hit. Ogre A rolls 16, margin +6, deals 12 damage, leaving Ogre B with 7 HP. Ogre B rolls 9, margin -1, deals 5 damage, leaving Ogre A with 14 HP. Ogre A wins. Subtract: 14 minus 7 = 7 HP remaining. Bloodied but standing.

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Obviously this is intended for NPC fights and mass combat, mostly. Most players do not want their PCs to be killed in a single roll, and that can absolutely happen here. But it can be used in a limited way even for PCs: if your fighter is attacked by a mob of goblins that could never realistically kill him, a single roll quickly tells you how much damage he sustains before cutting through them, and everyone moves on.

Chainmail magic: Spell Complexity, Counter spell, and more oddities

Chainmail* has several interesting ideas that have been "lost" in the transition to D&D. Studying them is fun and can provide many ideas for your D&Dish games. Today, we tackle magic, in three parts: Spell Complexity, Counter spell, and other curiosities.

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Spell Complexity

Spell Complexity is an optional rule where "each listed spell has a complexity value, and this value indicates how difficult it is to use such spell. [...] In addition, there may be a delay in the effect of the spell, or it may be totally negated due to some minor error or distraction. The table below gives the scores necessary for immediate, deferred (1 turn), and negated spell effects by the various levels of magic-users.".

In other words:

- Roll 2d6. Subtract spell level. Add half your level, round up (this is an approximation, CM units have names instead of levels).

- 8 or more means the spell is cast immediately. 6-7 means it is delayed for one turn. 5 means the spell fails. 

While I have written my own roll-to-cast rule for B/X, I must admit I'm enthralled by this one, simply because of the spell delay aspect. It adds another layer of excitement/tension and choice/tactics to everyone on the battlefield.

Now spell interruption is not only about initiative, but about a series of choices on both sides of the battle.

BTW, the book won't tell you what happens if you roll lower than 5; I first assumed the spell is lost for the day, but it could also be a spell mishap, etc. Look at the post I mentioned for more ideas. But, as mentioned in the comments, the table probably indicates that 5 or less means the spell fails. The notation is horrible but supposedly it is common in wargaming at the time.

Counter spell

"The stronger magician can successfully cast a counter-spell with a two dice score of 7 or better, while a weaker magician needs a score of 8, 9, 10 or 11, depending on his relative strength. A counter-spell fully occupies a magician's powers." 

In other words... you could employ a similar dice roll as the one describe above, adding your level and subtracting your opponent's level (half-level would be more precise, but I'd favor simplicity here).

CM does not delve into further detail; I assume the spell that is successfully countered is negated. I'm unsure if only delayed spells can be countered, but it would be fun if your delay allowed another magician to not only counter your spell but also cast a spell against you, etc.

Again, this adds another layer of tension and tactics to the game.

Other curiosities

"Wizards can handle magical weaponry. [...] Wizards can become invisible and remain so until they attack, they con see in darkness, they affect friendly and enemy morale as do Super Heroes [...]. Wizards are themselves impervious to normal missile fire but if they are struck by a missile from an enemy Wizard they must score 7 or better with two to survive."

They seems very powerful!

Wizards are also artillery. They can throw fireballs and lightning bolts (with effects similar to guns and catapults), which are not spells, so presumably they don't "roll to cast" and never run out. I like this approach and I added an "arcane artillery" feat to my Old School Feats.

A wizard - the highest level a magic-user can get - has only 6-7 spells. If we count fireballs, lighting bolts, and in visibility, we are not very far from one spell per level, which I like.

Also notice the lack of "Vancian" casting. No memorization. You just have a few spells that you can cast over and over until you fail.

Overall, I really like Chainmail magic. It is somewhat simpler and at the same time has more tactical depth than B/X, without getting to AD&D levels of complexity.

It doesn't require memorization, material components or specific casting times; the spells can be cast more often, but also can be delayed and countered. This seems to me as a superior alternative as it is more exciting than a list of requirements.

A B/X conversion?

How about 10+ means immediate casting, 5+ means delayed casting, and less than that you fail or lose the spell? This makes MUs lose some of their speed but not their power. Seems good for starting MUs, but as always they become too powerful at higher levels. As always, some fine-tuning is needed.