The Mass Combat Hack

Mass combat is handled by treating combatants as a single creature, calculating a combat scale, and applying a combat factor. The group led by a character will use the character's stats for tests and damage. The character's CHA stat is used for attacks. The INT or WIS stat (character's choice) is used for avoiding damage. A group can be led by only one character, but that character can be of any class.

Calculate Combat Scale

Combat Scale is determined by the size of the group. Use the chart below to determine the combat scale of each group.


Number in Unit 2 - 5 6 - 10 11 - 20 21 - 40 41 - 80 81 - 160 161 - 320 321 - 640 641 - 1280
Combat Scale x2 x3 x4 x5 x6 x7 x8 x9 x10

For example, a marauding band of 20 Goblin warriors is attacking a group of villagers. Consulting the chart, they have a combat scale of 4 or CSx4. The villagers have amassed a group of 30 to fend off the attack. The 30 villagers have a combat scale of 5 or CSx5.

Determine Stats

Goblins have 1 HD, so according to the monster damage chart, they do d4 damage. Per the monster entry, they roll 1d6 for hit points instead of 1d8. After rolling for hit points, the goblins have the following stats: HD:1, Hit Points: 4, Damage: d4, CSx4.

The villagers are led by a 2nd level Warrior with the relevant stats; INT 11, WIS 12, CHA 14. The GM rules that they are treated as 1HD for determining hit points and have no armor. Rolling for hit points, the result is a 5. The Villagers' stats are: CHA: 14, WIS:12, Armor Points: 0, 5 Hit Points, d8 damage, CSx5. CHA is used for attacks representing the Warrior's ability to get the villagers to obey his directions. WIS is higher than the Warrior's INT, so it was chosen for avoiding damage. The villagers do d8 damage per the Warrior's damage.

Determine the Combat Factor

The Combat Factor represents how the size of the two groups affect the outcome of the battle. If the character's group is larger than the opponent's group, they can do more damage and absorb more punishment. If the opponent's group is larger, the character's group will do less damage and suffer greater casulaties.

To determine the Combat Factor, subtract the opponent's Combat Scale from the character's combat scale and consult the chart below. The Combat Factor is multiplied to the damage done by the character's group and divides the damage done by the opponent's group. Any fractional damage is dropped. If the two groups have the same Combat Scale, damage is determined as normal combat without multiplying or dividing damage.


Diff CS -8 -7 -6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6 7 8 9
Combat Factor   1/16 1/12 1/8 1/6 1/4 1/3 1/2 2/3 * 3/2 2 3 4 6 8 12 16 24

The villager's final stats are: CHA: 14, WIS:12, Armor Points: 0, 5 Hit Points, d8 damage, CF: 3/2

Running Combat

Combat progresses per the normal rules with two exceptions:
- Different Stats are used for attack and defense
- The Powerful Foes rule is not used.

Recalculating Combat Scale and Combat Factor

After each round, reduce the size of the Combat Scale for both groups as Hit Points as lost. This may also change the Combat Factor.

Continuing with the villagers and goblins in our example, the goblins do 2 hp damage to the villagers. The villagers now have 3 out of their original 5 hit points. This means they have 3/5 the number of villagers. 3/5 * 30 = 18. As there are now 18 villagers, their new Combat Scale is 4.

Comparing the Combat Scale of both groups, they are the same. Consulting the Combat Factor chart, the villagers have a CF of 0.

Mass Combat Example: Villagers vs Goblins

20 Goblins -- HD:1, Armor Points: 0, Hit Points: 4, Damage: d4
30 Villagers -- CHA: 14, WIS:12, Armor Points: 0, 5 Hit Points, d8 damage, CF: 3/2

The character directs the villagers to set up formations to attack the goblins with rocks and pitchforks. Making a WIS test for initiative, the goblins go first. On the WIS test to avoid damage, the player rolls a 12. Argh! Rolling a d4, the result is 4. The villagers have a CF of 1. Dividing 4 (rolled damage) by the factor is 2 1/3. This rounds down to 2 points of damage. On a CHA test, the villagers miss doing no damage. Calculating casualties, 3 hit points remain out of 5 hp the villagers began with. 3/5 * 30 villagers means that there are 18 villagers left. Consulting the table, they are down to Combat Scale 4. Since this is the same as the goblins, the villagers have CF of 0. The goblins are unchanged.

Rolling a WIS test, the villagers avoid the swords of the goblins. With a CHA test, they strike home raining down stones from the rooftops as the second line advances to engage the goblins. Rolling a d8, a 3 is rolled. With no Combat Factor, the damage is not modified. Calculating casualties, the goblins have 1 hit point remaing out of their initial 4 hit points. 1/4 * 20 (the original number of goblins) = 5. Their Combat Scale is now 2.

The villagers are still at Combat Scale of 4. The difference between the Combat Scales is 2. Consulting the Combat Factor chart, the villagers now have a Combat Factor of 2.

The goblins regroup and dive into the group of villagers on the ground to avoid damage from the rocks above. A WIS tests fails and the goblins roll 4 points of damage. 4 divided by the combat factor of 2 yields 2 points of damage. The villagers press on, and succeed on a CHA test. The Warrior's quick thinking directed the rooftop villagers to attack from above. Rolling d8 for damage produces 3. When multiplying the Combat factor of 2, the final damage done is 6. The goblins have been vanquished! The 12 villagers that sacrificed their lives are honored with songs and feasting! The Warrior is hailed as a hero for saving the village!

Mass Combat Example: Knights vs Dragon

This system also works for armies against a very powerful foe.

The 100-strong Knights of the Crown stand ready against a Dragon. The GM rules that the knights are treated as 2 HD Warriors all with chain mail and large shields. They are CSx7. The dragon has CSx1 since he is alone. Calculating the difference between Combat Scales is 6. This give the knights a Combat Factor of 8.

100 Knights led by 5th level Cleric, WIS:17 CHA:15 -- CHA: 15, WIS:17, Armor Points: 10, Hit Points: 10, d6 damage, CF: 8
Dragon: HD:11, Armor Points: 10, Hit Points: 66, Armor Points: 10, Damage: 2 Claws (1d8), Bite (1d10), Breath Weapon 3d8, Spells: Shield, Charm, Web

The Knights win initiative and charge the dragon with their swords. The roll success! Rolling d6 for damage, they roll 5. With CF:8, that is 40 points of damage. This is reduced by the dragon's 10 armor points to 30. The Dragon is struck hard, and boils into a rage. The Dragon flies high above and breathes flames across their formation. Making a WIS test, the knights avoid the rain of fire.

With no loss of knights and the Dragon's CSx1, the Combat Factor is unchanged.

The knights charge again, but fail to penetrate the dragon's scaly hide! (Failed CHA test.) The dragon slashes the knights, raking their ranks with a vicious bite and sharp claws, (WIS test fails). The claw damage is 9 points and the bite adds another 8 for a total of 17. With the Knights 10 Armor Points, this is reduced to 7. Dividing 7 by a Combat Factor of 8, yields 1 point of damage (any remainder more than .5 is rounded up).  Calculating casualties, the knights are down to 9 / 10 of their original force, now numbering 90. Their Combat Scale remains unchanged.

The fallen knights will be commended for their valor, yet the stuggle continues...

The Last One Standing

At the GM's option, if the forces under the character's command fall, they make engage the enemy single-handedly.

Link to Sections 1 to 14 of the OGL

Section 15 of the OGL:


Open Game License v 1.0 Copyright 2000, Wizards of the Coast, Inc.
The Black Hack © 2016 by David Black
Additional Things © 2016 by David Black
M20 Mass Combat © 2016 Robin V. Stacey
Mass Combat for The Black Hack © 2016 by John Payne