Simple mass combat rules

[ericgrau]

A recent thread on mob combat gave me an idea on how to handle mob combat. Divide identical soldiers into groups of 20. Add up their HP. To resolve attacks of one group against another or against PCs, determine how many times one group would hit the other out of 20. That's how many hits they land. From there you may roll damage for all hits, take average damage times the number of hits (recommended for fastest NPC to NPC conflict) or take average damage for most hits and roll for the last 2-3 (this is almost as random as rolling for all of them). You might also randomize the number of hits by adding 1d3-2 (-1 to +1). If a group was damaged, subtract that HP from the group's total. Next comes the question, how much damage until the first soldier death? I ran a computer program to try it out and got the following results:

{table]Hits to die|Group HP lost until 1st death
2|15%
3|25%
4|30%
[/table]
"Hits to die" is about how many hits it takes to kill a single soldier using the damage from his attacker. Round up.

Every time the group is down the above percentage of HP a soldier dies and you steal one from a neighboring group. Then heal 5% of the group's HP. If a wounded (but not unconscious) soldier retreats and is replaced by an unharmed soldier, heal 2.5% instead. Repeat until the group is no longer is down by the 1st death percentage. Obviously if a single hit kills you should instead total up the number of hits and mark that many deaths instead of determining damage. Each dead soldier is replaced from a neighboring group and the group HP does not change. At the end of the round tally up the number of deaths (equal to the number of soldiers stolen from neighboring groups), get the new total number of soldiers and divide that into groups of 20. Some of the old groups will be kept (but now with 20 soldiers), others will be scrapped to fill the remaining groups. If you have a partial group leftover, then fudge it. i.e., a half group would have half HP and hit half as many targets. A group of 1-3 (or more, in larger battles) leftover might be ignored and used only to replace dead soldiers next round.

You could do the same thing with save based attacks. It may be helpful to record how many creatures fit in a spell radius ahead of time. And determine whether or not troop formations are staggered to reduce this number. Then you might say "17 out of 20 fail their save, you hit 5, so let's say about 4 fail the save and 1 passes." Or for smaller number of targets you might roll normally.

Optionally you might want to account for overkill; i.e. if excessive damage kills a soldier, leftover damage should not apply. This can be represented simply by reducing all incoming damage as follows:

{table]Hits to die|Damage reduction
2|25% (1/4th)
3|17% (1/6th)
4|12.5% (1/8th)
[/table]

Since large battles will have a lot of NPCs killing NPCs, it may be better to determine how much damage a group of one type can do to a group of another type ahead of time and make a table. That would save time during a session. Recording how much HP is 15%, 25%, etc. for each group ahead of time might also be helpful.

Thoughts? Is this simple enough? Oversimplified? Still too complicated? Did I ignore any problems?

[gkathellar]

First, an unhelpful comment:

Simple

I don't think that word means what you think it means.

Now, helpful comments:

A recent thread on mob combat gave me an idea on how to handle mob combat. Divide identical soldiers into groups of 20. Add up their HP. To resolve attacks of one group against another or against PCs, determine how many times one group would hit the other out of 20. That's how many hits they land.

While this does mean fewer dice rolls, it requires a lot of preliminary math and doesn't solve one of the essential problems of mass combat: that large groups of low-level enemies are not a credible threat. Also, what about groups smaller than 20? Or groups of thousands? That's a lot of groups of 20.

From there you may roll damage for all hits, take average damage times the number of hits or take average damage for most hits and roll for the last 2-3 (this is almost as random as rolling for all of them). If a group was damaged, subtract that HP from the group's total. Next comes the question, how much damage until the first soldier death? I ran a program to try it out and got the following results:
{table]Hits to die|Group HP lost until 1st death
2|15%
3|25%
4|30%
[/table]
Every time the group is down the above percentage of HP a soldier dies and you steal one from the neighboring group. Then heal 5% of the group's HP. If a wounded soldier retreats and is replaced by an unharmed soldier, heal 2.5% instead. Repeat until the group is no longer is down by the 1st death percentage. Obviously if a single hit kills you should instead total up the number of hits and mark that many deaths instead of determining damage. At the end of the round tally up the number of deaths (equal to the number of soldiers stolen from neighboring groups), get the new total number of soldiers and divide that into groups of 20. If you have partial groups, then fudge it. i.e., a half group would have half HP and hit half as many targets. A group of 1-3 might be ignored.

So you have to separately track the group's percentage of HP, the group's number of soldiers, and the group's reinforcements? That seems ... inelegant, especially when we're dealing with large numbers of troops. I'm still tracking individual troops, so why shouldn't I just track individual troops?

You could do the same thing with save based attacks. It may be helpful to record how many creatures fit in a spell radius ahead of time. And determine whether or not troop formations are staggered to reduce this number. Then you might say "17 out of 20 fail their save, you hit 5, so let's say about 4 fail the save and 1 passes." Or for smaller number of targets you might roll normally.

Optionally you might want to account for overkill; i.e. if excessive damage kills a soldier, leftover damage should not apply. This can be represented simply by reducing all incoming damage as follows:

{table]Hits to die|Damage reduction
2|25% (1/4th)
3|17% (1/6th)
4|12.5% (1/8th)
[/table]

Since large battles will have a lot of NPCs killing NPCs, it may be better to determine how much damage a group of one type can do to a group of another type ahead of time and make a table. That would save time during a session.

AUGHAAGJSNGIEANSDF MATH.

[ericgrau]

Lol.

You don't have to track the number of soldiers in each group, because after each round they get regrouped into groups of 20. You do have to tally the number of deaths, but that's a total for all groups not per group. Per group you only need to bump their HP back up to above the "first death" threshhold at the same time that you're tallying deaths. The damage reduction rules are optional; they don't make a huge difference. The rest is as you say.

If it would make any difference I could change the groups into swarms with tables or die roll amounts telling you how much damage they do against X AC when the group has Y HP left. That's more work for me but these would not need to regroup. The one and only thing you'd track for each group would be HP. On their turn you'd check a table for what dice to roll for damage based on how many HP they have left. But, ya, dunno if that'd be any better.