Before Halloween, Wizards of the Coast took the hype level for their new D&D supplement, Xanathar’s Guide to Everything, and turned it up to 11 by releasing the table of contents. Now it’s known what’s in the book and what we can expect to use in upcoming games once the book is released on November 21st. Also important though is what didn’t make the cut. New classes like the Mystic and the Artificer were left behind, and so was a set of mass combat rules. Even if the mass combat rules have not been built into a sanctioned product yet, the version released in Unearthed Arcana has some neat uses and is definitely worth considering for use in your game.
Mass combat is something that sits on the periphery of a lot of combat-heavy role-playing games, especially fantasy games. After all, every GM running a game like D&D has at least thought about what it would take to run their own Helm’s Deep or Battle of the Bastards. Though it sounds like a really cool element to add to a game, there are two functional difficulties that hold it back. First, it requires an additional level of abstraction, and second, it takes the spotlight away from the players. A good mass combat system will make large battles both a source of conflict and challenge for the players as well as a randomizer that will add to the story. It will also do this without giving the GM too much extra work.
So let’s look at the Unearthed Arcana mass combat system. At its core, the mass combat system simply converts the challenge rating of a contributing soldier or monster into a battle rating. The battle rating of an army is the sum of all creature battle ratings in that army. Once armies fight, they make opposed checks, with each side taking casualties according to their margin of success. There is also a morale rating, which is first used for calculating initiative. A check against the morale rating is also made if a unit takes heavy casualties, to see if they stand their ground or flee. In combat each unit can choose from five actions: attack, defend, dash, disengage, and guard. The latter two moves make it clear that mass combat is meant to be tracked on a map (a hex map, specifically), as they are moves dependent on facing and adjacency of units. The actual mechanics of how creatures fight are glossed over, absorbed into the battle rating. Similarly, battlefield conditions are collapsed into the elegant advantage/disadvantage system instead of being turned into a table of different modifiers.
Outside the combat system itself, there is guidance for how to assemble units. Each unit, which is assumed to occupy a 100 foot hex, gets 400 size units, which are equal to a tiny, small, or medium sized creature. So a unit may be 400 human soldiers, or it might be 25 elder dragons, but in terms of resolving the battlefield, both of those would take up the same amount of space. If you’re playing out the battle these rules are immensely helpful, but if using the mass combat rules for background resolution, I might fold each side into one big army to speed up calculations. If it’s a battle the characters are participating in, though, definitely use those unit rules.
Character involvement in large fights is interesting, and the rules give two possible angles for direct character participation in a mass battle. The first is if characters are taking on the army themselves. In this case, the standard mob rules in the Dungeon Master’s Guide come into play. It’s important to note however that character combat time is slower than mass battle time (6 seconds per turn versus one minute per turn), so the surrounding battle essentially pauses while the characters fight. If you were a very precise GM you could roll for the adjacent units every ten turns, but I think this guide is correct in assuming that level of detail is unnecessary. The other angle for character participation is fighting with a friendly unit. In this case, the characters are allowed to take actions against an enemy unit, and will alter their battle rating if they eliminate any enemies. This abstracts the character abilities more than if they were fighting alone, but does still lend weight to their presence, especially if the enemy unit has big creatures or if the PCs can use area-of-effect attacks. There is a sidebar about abstracting a PC as if they were commanding a unit, but these rules really want to treat the PCs as unique, and don’t offer much in the way of rules for being commanders.
The “characters-as-commanders” paradigm is the first use case many GMs will think of for mass combat, but here it falls a little short. The commander’s Charisma score provides a modifier to morale, but a) that’s the only way a commander would alter the outcome of the fight in the rules, and b) since that rule applies at the unit level, it may not technically apply unless the commander was in the field, where it might be more interesting to use one of the abovementioned character treatments. Unfortunately, there’s not much to be done here without modifying the base game: the 5e skill list doesn’t include Leadership, Tactics, or anything that would apply to commanding situations. It is definitely possible to use some of the existing skills to perform military tasks (Perception and Persuasion come to mind), and this is also a space where feats may do the trick (though feats specifically suited to leading armies may be of very limited use in most campaigns!). Still, the lack of any base rules around warfighting hamper what the Unearthed Arcana authors could do in terms of turning a mass combat system into a player-facing wargame.
The mass combat rules provided in Unearthed Arcana are a solid way to abstract large battles. Without adding many additional rules this system makes it easy to resolve a huge battle and uses morale to great effect, to the point where I’d strongly consider adapting the morale rules for smaller combats (a quick internet search reveals I am far from the only person trying to put morale back into D&D from earlier editions). The lack of rules around commanding armies is understandable, but a bit of a sore point with me personally as I am currently writing up a D&D game with heavy domain-based elements. If it were up to me, I’d take mass combat, a deeper dive into the building construction rules in the core books, and a dominion system similar to (but less complicated than) the rules put forth in BECMI D&D, and release a “Kings and Generals” supplement that integrates all three. A clearly optional supplement for those who aren’t interested, with some good detail and interlocking systems for those who are. Combine these with the additional rules for downtime activities, random encounters, and magic items coming soon from Xanathar’s Guide, and you’d have a treasure trove of resources for running a sandbox game. Even if the mass combat rules don’t meet all of my personal desires, they provide a solid foundation for running large battles quickly and without too many headaches.