Improved Mass Combat Rules (Part 3: Design Notes for Unit Purchasing) | New Rules for Dungeons & Dragons Fifth Edition

This is the third installment of the mass combat rules series. While writing the basic rules for the system, I realized that there were no rules for purchasing units. However, I think there’s a pretty easy way to do it as I’ll detail below.

This is an attempt to improve upon the mass combat rules that Wizards of the Coast released a while back, which is a little too simplified for its own good and kinda blah.

Playtest Content

The material here is presented for playtesting and to spark your imagination. These game mechanics are in draft form, usable in your campaign but not refined by final game design and editing. They aren’t officially part of the game.

Constructive feedback is welcome and appreciated in either comments or social media. If you can give me a valid reason with examples why something is off, 9/10 I’m likely to make changes to the content and credit you for doing so. Otherwise, feedback without anything to back it up gets ignored (or at most a smile emoji like this 🙂 ) Thanks!

Design Notes

Here are my notes for this build.

Before the Build

To keep the game balanced between the DM and the PCs, there needs to be some sort of unit purchasing system. The system can’t work the same as level versus CR from Fifth Edition, because the PC’s have allies on their side. It’s a war game at this level, therefore it should designed as such. In other words, the players could lose a battle and not be adversely affected (other than roleplaying repercussions, of course). Therefore the typical asymmetrical style of play is not necessary.

Fortunately, we’ve got a rough model within the CR and XP system that can help me figure out what to price out units.

Since the units more or less scale in a linear fashion, the best (and probably crudest) way is to use the unit’s XP as purchasing points. The other thing to consider is that the armies must be balanced in unit size. If they aren’t, we need to defer to the Encounter Multiplier table on page 82 of the DMG.

Here’s why. Consider this situation: two armies have 700 points to spend on their troops. The DM is playing goblins and buys 14 units of goblins. The player is playing humans and buy 1 unit of knights. Which is better? Obviously, the goblins, because they are way more powerful.

If we do a little math using the Encounter Multiplier table, we know that roughly 6-7 goblins are in line with 1 knight.

Therefore, armies must be purchased in “battalions” that roughly equal the same XP.

A battalion can equal 1 or more units. Now we don’t have to use any sort of XP. We just say that you can purchase X number of battalions for your battle.

So a battalion of 4 knights units would normally have an encounter XP cost of 5,600. If we use that same budget to purchase a battalion of nothing but goblins, we’d have 28 goblins in the battalion.

That seems kinda nuts, right? Of course, knights are pretty tough, so I’m sure the math checks out (and probably looks cool AF when played out).

But what we can do is mix up the types of creatures in the battalion. So instead of just 28 goblin battalions, we’ve got 10 units of goblins, 5 units of gnolls, and a 1 unit of ogres. We can probably divide things up a bit more, too. We can take 2 of the goblin battalions and mount them on worgs. And then we’d have 4 units of goblins. We’ve lost some of our goblin units so our Encounter Multiplier will drop, so I’m going to toss in another ogre unit. It all adds up to 5,700 XP, just a little more than the knights.

So the humans have a battalion consisting of:

  • 4 units of knights worth 2,800 XP (700 x 4)
  • x 2 XP multiplier for 4 units
  • Total: 5,600 XP

And the goblins have a battalion consisting of:

  • 2 units of goblins mounted on worgs worth 300 XP ((50 + 100) x 2)
  • 4 units of goblins worth 200 XP (50 x 4)
  • 5 units of gnolls worth 500 XP (100 x 5)
  • 2 unit of ogres worth 900 XP (450 x 2)
  • x 3 XP multiplier for 13 units
  • Total: 5,700 XP

So in theory, these are two pretty well-balanced armies. If it doesn’t seem that way at first glance, remember that the knights have some pretty strong AC, they’ll have 10 unit hit points each (for a grand total of 40), and they can deal 4 unit damage in a round (for a grand total of 16).

On the goblins side, the goblin worg-riders have 6 unit hit points each (for a grand total of 12), the gnolls have 4 unit hit points each (for a grand total of 20), the base goblins have 1 unit hit point each (for 4), and the ogres have 11 unit hit points each (for a grand total of 22). This puts the goblin horde at a total of 58 unit damage. It’s about 50% than the knights, but remember, they don’t have the same high AC that the knights do.

For attacks, the goblins, gnolls, and goblin-worg riders only deal 1 unit damage each (for a grand total of 11 unit damage). And the ogres only have 2 unit damage each (for a total of 4). That puts the goblin army at 15 unit damage per round, 1 unit damage less than the knights. It might be a tough battle, but if the knights can take out the ogres early on and stay outside of the range of the enemy, they stand a pretty good chance at winning.

Individual Creatures

When incorporating an individual creature, I’ll probably want to reverse engineer a unit as if it were the finished result of a mass combat unit template.

I can do this by first dividing the creature’s hit points by 20 and round up. That’s its unit hit points. And then, I have to remultiply that number by 5. So for example, if I do this with a Frost Giant, I end up with 35 hit points.

Next, I have to do the same thing with its attack. When using the optional huge/gargantuan rule for big creatures attacking smaller units, we can take the individual creature’s average attack and divide it by 8. Then, we multiply that number by 5. So for our frost giant, we end up with 15 average damage per round.

Those two numbers will help us build our “mini-creature”. Think of it this way: if the individual creature were a unit, the end result would be one member of that unit.

All we have to do now is plug those numbers into the monster statistics by challenge rating chart to come up with our experience cost. Our frost giant has immunity to cold, so that doubles its virtual XP to 70 which bumps further because of its 15 AC. This puts it at a defensive CR of 1. Next, I take its 15 damage and then bump that up 3 times to CR 5 since it has an attack bonus of +9. The halfway point between those two CRs is 3, so the “mini-Frost Giant” is a CR 3 creature.

Therefore, an individual frost giant has a cost of 700 XP in battle. In other words, a unit of knights can stand toe-to-toe with one frost giant.

TL;DR Version

Okay, thanks for bearing with me while I worked out all the math. Here’s pretty much everything I figured out for purchasing units.

  1. Each battle will have a set mass combat XP budget.
  2. The players and the DM use XP budget to purchase units.
  3. The mass combat XP cost for a unit is the same as the unit’s base creature’s XP reward.
  4. In order to determine the mass combat XP costs for individual creatures, you must calculate their “unit cost”, essentially how the individual creature would rank if it was a unit.
    1. Divide the creature’s average hit points by 20 (round up) to determine its unit hit points. Then multiply that number by 5. That is its virtual hit points used only to calculate its mass combat XP cost.
    2. Divide the creature’s average melee attack by 8 (round down) to determine its unit damage. Then multiply that number by 5. That is its virtual damage per round used only to calculate its mass combat XP cost.
    3. Use the Monster Statistics by Challenge Rating table on page 274 of the DMG to calculate its virtual challenge rating using its virtual hit points and virtual damage per round (all of the normal rules for determining challenge rating still apply).
    4. Use the virtual CR to determine the individual creature’s mass combat XP cost.
  5. The normal XP encounter multipliers outlined on page 82 of the DMG are used to balance the units.

Calculating the cost of heroes

Of course, there are other factors to consider here, too, such as players and heroes. But the same rules apply. Since heroes get actions, I feel like it makes sense to double their mass combat XP cost (for now at least) once I figure out what it is.

First, determine the player’s unit hit points. So if a 9th-level Fighter character has 60 hp than its virtual hit points will be 15 for the purpose of calculating its mass combat CR. However, the fighter has no abilities that allow it to affect units, but it can use its Intimidation power to challenge a unit’s commander and fight it individually. I don’t see this happening a lot, but I think it probably warrants at least 5 virtual damage per round. The fighter’s wearing plate and is carrying a shield and its attack bonus is +11. So its mass combat CR is 2, making it worth 450 mass combat XP.

If an individual creature can deal area of effect damage, then it will need to be calculated differently. Let’s say that a wizard has 3 fireballs in its arsenal. Each fireball deals an average of 28 damage–or 5 unit damage. However, the average battle should last close to 10 rounds. That means the wizard will get an average of 1.5 unit damage from its fireballs. Then, the wizard still has four uses of burning hands. Burning hands, on average, will hit roughly half a unit. That’s worth at least 1 unit damage. So that’s another 4 damage. And so on until we’ve mapped out the most damage the wizard can do each round. Then, we factor in its hit points and determine its mass combat CR just as before.

This is something else I’ll probably make a chart for just to make life easier.

Okay, so here is a summary of what I’ve added here:

  • Heroes (including players) are calculated using the same rules for individual units.
  • As long as a hero can challenge a unit, it is awarded at least 1 unit damage or 5 virtual damage per round when calculating its mass combat CR and mass combat XP cost.
  • Heroes with area of effect powers are much more powerful. To determine their mass combat CR and mass combat XP cost, you will have to determine the most optimal way for it to attack over the course of 10 rounds.

Using leadership points to buy heroes

In addition to all this, I should consider the advantage that high Charisma characters have in mass combat since they can control so many units. Each Charisma modifier is probably equal to a bump in XP modifiers. Or at the very least, the two armies should be able to match one another with leadership points.

A leadership point will probably be 1 + the hero’s Charisma modifier (minimum of 1).

So if a party of PCs has 5 characters and their Charisma scores are 9, 10, 12, 14, and 18, that means their total leadership points are 14.

To match the PCs, the DM could build an army that has seven leaders, each with a +1 to its Charisma modifier, or one leader with a +8 charisma modifier that has one general that has a +4 bonus to its Charisma modifier.

Because the range of leadership is limited, I’ll probably need to toss in some sort of multiplier there, too, similar to the way that building encounter XP works.

Another summary:

  • Heroes should be measured by leadership points. An individual hero’s leadership points equal 1 + its Charisma modifier (minimum of 1).
  • Both sides try to match each other in leadership points.
  • Having more heroes warrants a multiplier to leadership points, similar to the way encounter experience works.

Thanks for reading my ravings!

Sometimes, when I’m working on a new set of rules, it’s a lot better if I just write it all out so I can have it in front of me.

Now that I’ve got all this out, I just need to take it and translate it all into rules.

Let me know what you think in the comments!

And you haven’t already, be sure to grab a copy of the Improved Mass Combat Rules PDF that introduces the first part of the rules.

Art by Wizards of the Coast.


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