Modron Tactics

I was a huge math nerd as a kid. I think I must have been just 5 or 6 years old when I first got my hands on Flatland, and I drank it up like a parched man in a hot desert (having no idea until many years later that it was an allegory for classism and sexism in Victorian England), and the discovery of a quasi-sequel called Sphereland (sadly, not in print right now) delighted me even further.

So maybe you’d expect me to be more into modrons than I am. But when a reader recently told me he planned to run a campaign in Mechanus, the plane of pure law, and thought he wasn’t doing the modrons justice, I had to confess: I hate them. I have a great appreciation for silliness, but modrons have always struck me as just too silly, like whoever came up with the idea of Mechanus envisioned it as something out of The Phantom Tollbooth or Donald in Mathmagic Land.

Modrons are constructs, automata with vaguely mathematically inspired bodies and weirdly humanoid faces (with, in the illustrations of the fifth-edition Monster Manual, disturbingly full lips). The more advanced the modron, the more it can multitask, and the more authority it has over other modrons. All modrons possess natural armor, above-average Dexterity, 120 feet of truesight, and the features Axiomatic Mind and Disintegration.

One of the many peculiarities of modrons is that they’re denizens of an outer plane, yet their challenge ratings top out at 2. How many low-level adventurers are going to travel to Mechanus? I wonder whether these creatures must exist at least primarily for the sake of background decoration. They’re not going to pose a challenge to the player characters who encounter them except in great numbers—legions.

The monodrone is the simplest, lowest-level modron. It can fly, but it doesn’t have any way to avoid opportunity attacks, so the tactic of holding station in the air, flying down to attack and flying back up is suboptimal. Instead, it uses its flying movement to make ranged javelin attacks over opponents’ cover, traverse vertical distance and ignore difficult terrain. (Not that there’s any difficult terrain in Mechanus.)

Although it has average Wisdom, its Intelligence is animal-level: it chooses targets indiscriminately and has no ability to adapt to changing circumstances. Whatever its orders are, it follows them to the letter.

It carries a dagger and a javelin, but note that the attack and damage of the javelin attack are based on its Dexterity. Javelins are not finesse weapons, so a monodrone using a javelin as a melee weapon should actually have +2 to hit, not +3, and do 1d6 piercing damage, not 1d6 + 1. Also, logic dictates that a weapon you throw is a weapon you no longer have. So we have a simple formula for monodrone combat: approach to 30 feet, throw the javelin, then close to melee range and fight with the dagger from that point on. If at any time a monodrone manages to defeat or displace its opponent, retrieve javelin, GOTO 10.

Monodrones have no independent judgment, and since modrons exist in infinite supply, they have no self-preservation instinct. A damaged monodrone follows its instructions until it’s destroyed.

Duodrones are only marginally more intelligent than monodrones, and they can’t fly. They can attack twice in one action, but they must do so with the same weapon: either two javelin attacks or two pummeling attacks, not one javelin and one pummeling. Also, just as with the monodrone, the duodrone’s Dex is slightly higher than its Strength—but unlike the monodrone, the duodrone carries no finesse weapon for melee combat.

For this to make any sense at all, I think a duodrone has to carry several javelins into battle, and the number must be odd (not even, and you’ll see why in a moment). Historically, in Classical times, soldiers carried three to five javelins onto a battlefield in their off hands or—rarely, and only toward the end of the period—in a quiver. So let’s give the duodrone five javelins, because in the illustration, its fingers are long and skinny; it can probably hold a big bundle.

When combat begins, a duodrone approaches to 30 feet and throws two of its javelins. If its opponent closes with it, it uses one of its remaining javelins as a melee weapon (remember to change the attack modifier to +2 and damage to 1d6); if not, it hurls two more, and at that point it still has one remaining that it can use for melee fighting. A duodrone can fight with its fists, but that doesn’t mean it should. A javelin does a bit more damage, so it will prefer to have one left over.

Like the monodrone, a duodrone will retrieve its thrown javelins whenever there’s a break in the action—but only if it can pick up two that have landed in the same person, place or thing. Picking up just one javelin would mess up the duodrone’s system. Also like monodrones, duodrones don’t retreat, no matter how much damage they take.

Nothing distinguishes a tridrone from a duodrone except its Multiattack (three attacks, meaning it always wants to carry 3n + 1 javelins—we’ll start it off with seven, since it has two extra hands to carry them in) and its near-average Intelligence, which allows it to adapt to a changing situation. Tridrones still won’t retreat to save themselves, but they will position and reposition themselves on a battlefield to take advantage of terrain, cover, chokepoints and other features with potential tactical benefits, and they’ll order lesser modrons to do the same. They’ll also respond appropriately to obstacles and hazards created by their opponents. However, they lack the Intelligence to create tactically beneficial features, obstacles or hazards themselves; they can only take advantage of ones that already exist.

Monodrones and duodrones aren’t intelligent enough to Disengage independently, but with a tridrone on the field to give the order, they can hear it and obey. Tridrones will cover the retreat of monodrones and duodrones that have Disengaged to take a new position. Also, it takes at least a tridrone to recognize an attack that does extra damage to constructs, such as a mace of smiting. Once an enemy makes such an attack, a tridrone will focus all its attacks on that enemy and order the other modrons under its command to do the same.

Quadrones are archers whose Dexterity and Multiattack both strongly favor ranged attacking over melee, so unlike tridrones, quadrones will lead from the rear, not from the front line. If someone needs to run interference, quadrones will order tridrones to do that. To the fullest extent possible, quadrones will maintain position between 35 and 80 feet from the nearest opponent, someplace with a good view of the whole battlefield and as much cover as they can get. From there, they’ll rain arrows down upon their foes, at a rate of four shots per turn. Twenty is a good number of arrows to give them.

When a quadrone runs out of arrows, five combat rounds have gone by, and that’s enough time for a quadrone to realize that things are not going as they should. At that point, they’ll order a tactical retreat toward a location with more modrons, including more quadrones, with any surviving tridrones in their unit acting as rearguard.

Pentadrones, despite being at the top of the modron hierarchy (as far as the Monster Manual goes, at least—we can hypothesize the existence of infinite types of modron), are brute fighters. If you’re using a battle grid, remember that pentadrones are Large creatures, so they take up more space.

Pentadrones march right up toward the front line of combat, let loose a cone of Paralysis Gas as soon as they can catch at least three enemies in it (not having the Intelligence to direct it specifically at enemies who look more susceptible to it), then start whaling away with their five arms, targeting those who have not succumbed to paralysis. They leave paralyzed targets to the lesser modrons under their command, which need advantage more than the pentradrones do and which are less equipped to battle those tough enough to make their Constitution saves. They continue attacking with their arms until their Paralysis Gas recharges, at which point they use that weapon again.

Pentadrones, like tridrones, will cover the retreat of lesser modrons if such a thing becomes necessary, but even they don’t retreat simply because they’ve taken serious damage. They order a retreat only if combat lasts more than five rounds, at which point the quadrones under their command will have run out of arrows.

When pentadrones lead a battle with other modrons under their command, monodrones, duodrones and tridrones will forgo their ranged attacks in order to seize the opportunity of attacking a paralyzed opponent at melee range for the “every hit a crit” benefit. When there’s no paralyzed opponent within their movement distance, they go back to their normal javelin-hurling routine, if they have any javelins left.

Finally, let’s talk about why lawful neutral beings are engaging in combat at all. This is a topic I’ve discussed before, when analyzing myconids. Lawful evil beings will want to kill trespassers by default, but lawful neutral beings are interested in maintaining order by the simplest, most straightforward methods available, and fighting is rarely simple or straightforward. Their default disposition toward strangers is indifference, not hostility. They’ll leave your PCs alone unless and until the PCs break the modrons’ rules or start causing a ruckus.

Unfortunately for the PCs, modrons aren’t equipped with features that would make them good at grappling. They can choose to attack to subdue rather than kill (see “Knocking a Creature Out,” Player’s Handbook, page 198), and I think this would be consistent with the values of the plane of pure law. Why kill what you can capture and put on trial? Trials are probably the pinnacle of public entertainment in Mechanus.

But also note the fine print on that page: only melee attacks can be nonlethal. Duodrones and, especially, quadrones are optimized for ranged combat. Small problems can be dealt with by monodrones that can swarm troublemakers and bring them back as captives. But a problem too large for monodrones will often involve modrons that aren’t going to compromise their combat effectiveness to avoid killing their enemies. And the modron method of solving problems is simple: throw more modrons at it. Mechanus never runs out.

Next: displacer beasts.

22 thoughts on “Modron Tactics”

  1. There are some (semi-)homebrewed stats and fluff for higher-grade modrons in a 5e conversion of The Great Modron March (which does indeed include legions, starting at about 10000 modrons) over at . Have you seen it, and if so, do you have any thoughts on it?

    Also, does the disintegration/promotion of modrons and their inability to communicate with those more than one rank away have any bearing on their behaviour?

    1. The only way I see Disintegration affecting modron tactics is that a duodrone or tridrone that can’t get at its own thrown javelins will unhesitatingly pick up ones that were thrown by a different modron. As for promotion, since this isn’t in the stat block but rather in the flavor text, I think you can’t assume that a modron gets promoted in the same place as the one that was destroyed. The newly promoted modron could pop up anywhere. It’s certainly implied by the flavor text wording that the replacements for all destroyed monodrones pop at the Great Modron Cathedral and have to travel to their assigned locations from there. I kind of wish this phenomenon were explained more clearly, because if the writers meant for the new modrons always to appear in the same place as the destroyed ones, that could certainly influence how they’d fight. But that, I think, would also necessitate their having much higher CRs, since for all intents and purposes, they’d be indestructible—every time you killed one, a new one would appear, at full strength.

      The inability to communicate more than one rank up or down wouldn’t influence their strategy, but PCs who realize this fact can exploit it to create disruption in the modrons’ ranks by taking out the middlemen first. For instance, if a tridrone is trying to communicate a withdrawal, and the PCs kill all the duodrones before they can pass the word along to the monodrones, the monodrones will then fail to obey the tridrones’ orders, never having received them from the duodrones.

      1. The way I interpret promotion, it’s Primus who ultimately decides which lesser modron gets promoted to replace a destroyed one, within their networked hivemind. (These guys are all about Law so it’s can’t be random right?)

        So if a fight is going on and the higher ranking modrons are being taken down, of course Primus is going to promote withint the remaining ranks at the scene.

        That being said, the promoted modron doesn’t appear out of thin air, not does it teleport to the location where the battle is taking place. It remains where it was and just upgrades. So, the stream of modrons in a given location is not endless – it’s limited by the number of modrons present who can be upgraded.

        If the party focuses on the middlemen, they will end up fighting more middlemen until all the lower ranks are either detroyed or upgraded.

        But that’s just my interpretation. I agree some more eexplicit instruction would be welcome here. IN particular, not making it explicit whether or not this promotion can happen in the middle of a battle seems like a pretty big oversight.

  2. *Please cease reading if you live in Brabant or you know a player who wishes to play as a potplant.*
    One of your issues with modron is how they are to low CR to be dangerous by the time you go planewalking. I agree. That is why in the campaign I’m planning, I’m not using them on the outer plane of Law only. This is my reasoning: Most planars seem to want to turn the entire multiverse into their respective plane. They just don’t get to it, for varying reasons:
    Demons want to break out, but gates outward are rare, and wherever they go the locals will focus on them with a vengeance, and they can’t get an organized force going. Devils want to kill Demons first, fixing them in eternal war. The good beings are too nice to do it via conquest. I couldn’t find anything about chaotic neutral planars, but I imagine that they are weaker than Demons and also not organized enough to take over.

    Modrons however, are the only beings who are organized, numerous, not bound to their dimension and not caring about those in the other planes. Thus, they establish bases in the prime part of the setting (A continent-spanning underground Labyrinth) all the time, trying to get a hold on the Material. Natural gates to the planes exist, although rare, in the labyrinth and thus the modron can build huge areas of influence around these, where they slowly replace everything to be the order they so desire. Thus, they can be fought before planes-walking, as the PC can simply stumble upon them while exploring the maze, and they are the only race from neither the Material nor the Underdark to build trade routes, outposts and hubs throughout it. The only limiter to their influence is the amount of modrons that can be built and transported to the needed locations.

  3. I’m no D&D historian, but I always assumed that modrons were invented for an adventure concerning The Great Modron March, meaning that adventures would encounter modrons on the Material Plane, not their home, Mechanus.

    1. Modrons were actually introduced in the AD&D Monster Manual II, even before the old Outer Planes cosmology was overhauled. The Great Modron March was written for the second edition.

  4. I disagree that modrons would fight to subdue so they could put people on trial. Trials are about guilt or innocence, and intent, which seems much more a Lawful Good thing.

    Instead, I see modrons having a bit that flips from non-dangerous (ignore) to dangerous (kill).

    1. Trials are about rules and process. That’s law in a nutshell.

      Even devils will put people on trial. Those trials will simply be rigged in favor of the guilty and against the innocent. If that’s not obvious to you, you’ve never watched our own justice system in action.

          1. Possibly, but if the devil feels it can further its own ends by making sure that this probably-found-innocent person can *definitely* be found innocent, then it would do that. Imagine the acclaim that could be won if Gregory the Good is so worried about the outcome of a case that he’d treat with a devil to make sure he stays free.

        1. I think in terms of trials, for Lawful Evil it’s going to be about who can manipulate the process best. Think sudden surprise witnesses, heavy appeals to emotion and straight up jury tampering. Your chance of getting off will be down to how well you can do this. It will be about swaying public opinion both in and out of the court room. Devils will certainly have a home court advantage for this, but it can be done, although you’ll probably need to get out of there sharpish (cf The Devil & Daniel Mouse).

          For Lawful Good, it will be about intent. Trials will revolve around what was in your heart, mitigating circumstances, good character and if there was a greater good (cf pacifists damaging warplanes). You’d be unlikely to get off scot free, but you can angle for leniency.

          I still think modrons attacking to subdue is a reach, but assuming you get to the trial stage then Lawful Neutral is going to be about the process, but how much help you get in understanding the process will be down to your DM. This could range from a simple finding of facts with one or a couple acting as judges to examine evidence and call testimony, all the way to a kafkaesque nightmare where you’re still trying to work out what they’ve charged you with as they sentence you (just because you don’t know the system doesn’t mean the system doesn’t know you). You may get you off on a technicality (especially if you can mess with the paperwork).

          What I don’t think you’ll see is a jury trial. If one, or a couple, of modrons is unable to make a decision they’ll just kick it up to the next level of modron.

  5. Lawful does not mean good.
    Good does not mean Nice.

    Modron’s are truly Lawful because they are, almost literally, cogs in a machine. I would argue that although their intelligence is baseline human normal, it doesn’t mean it is like ours. It is intelligent enough to open a door, manipulate an object, or understand the function of and use a tool, but at the lower tiers of modrons, it knows Modron language, it knows that things are either a Modron that can give you commands or you can give commands to, and anything that bars the completion of a task is to be removed.

    Mechanus is a place where you are built to do your role. Otherwise, you have no purpose. Think of the robots in Wall-E before the titular character ruins it for each and everyone of them creating rogue AI, or in this case Modrons. There are no trials. You do your task. Your task is finished, you are assigned a new task. You would never think of not doing your task. If you are not able to do your task, you are eliminated and replaced. (Rogue modrons are hunted down. according to the march I believe that rogues fear being seen by their former brethren).

    A monodrone can only follow one instruction. That instruction is Law to the monodrone. Anything that goes outside of said instruction is Not Law. The higher the modron, the more Laws it can take (duo takes 2, tri takes 3, etc..) Its also known that anything above mono usually is left with a free law to take its actions as it sees fit.

    A duodrone is tasked with gathering magic items in an area and bring them back from a tridrone.
    it is sent with 10 monodrones to search an area to complete this task.
    The duo gives each mono a section to search and to find any magic items and report back. One mono finds the PCs and reports back to the Duo.
    Now that an item has been found, the Duo will take all of its Monos and go get the item. When they meet the party, the Duo has enough intelligence to see that the PC is not Modron. It will command the PC to hand over the item (in modron). It will most likely attempt the command again. Now that the PC has not provided the item it will most likely fall into 1 of 2 things.
    1) realise that this thing is not Modron and rogue so must be removed or,
    2) instruct a Mono to go grab the item so they can return to the Trio.

    Either way is going to end in a fight to the death for the Modrons.
    The other way I like to think of them is like the Borg from Star Trek. They are Evil to sentient races, but they just want to see an efficient universe.

    1. I would actually go one further. Monodrones can only take one command, search and report are 2 commands. A tridrone would send a duodrone with 12 monodrones (because lore says each duodrone starts off with 12 monodrones to command). the duodrone would then marshal the monodrones into a row, and order them to search in a line, with itself in the center of the row, executing it’s two action of acquire object and interpret orders. Duodrones are not smart enough to take things like motion into account. If they ran directly into the PCs, then your 2 potential actions apply, but if the PCs are not directly within their search pattern, which can be no more than 240 feet across at maximum for the duodrone to remain in communication, they would never be encountered.
      Alternatively, a tridrone would more likely command it’s 12 duodrones and 144 monodrones in person. I think 11 of the duodrones would search as stated above, while the remaining duodrone and it’s 12 monodrones would be conscripted for conveyance. The monodrones would carry the tridrone and the duodrone, who would interpret the tridrones orders to move for the monodrones. The tridrone would then survey the area, and when it saw a duodrone halt or engage in combat, it would order the duodrone to order 10 of it’s monodrones to each fly to one of the other, not in combat duodrones, with recorded instructions on where the stopped duodrone was. the squad would then regroup.

      the big thing is that “one simple action” and “two simple actions” + supervision limitations on the least two drone types. They can’t think or decide at all, only follow orders. and, they can only follow incredibly simple orders. Even the tridrones have no more intelligence than an unusually obedient 2 year old. Unless the situation was of minimal importance, there would likely be at least a quadrone on the scene, commanding some tridrones, a bunch of duodrones, and a small horde of monodrones, simply because modrons don’t function well on their own. There’s a reason that they generally only go out in a single massive army one ever two hundred eighty some years.

    2. This gives me a nasty idea. The party have plumbed the depths of the dungeon and defeated the bbeg. They’ve looted the treasury but are low on resources. As they start to leave they hear a mechanical voice say ‘magic items detected’…

  6. While I do mostly agree with the tactics here, I feel the need to point out that the Monster Manual contains the section ‘ammunition’ on page 11. So instead of using only a single javelin, modrons carry 2d4 of them. Unless, of course, we argue that javelins are to large to carrie in large amounts, which would also be possible.

  7. Curious on your thoughts on this homebrew–what if Modrons were run more like a Napoleonic army (swap muskets for javelins and bayonets for daggers)? Monodrones and Duodrones seem pretty good line infantry/light infantry and Tridrones could manage things more like artillery and cavalry with Quadrones being like the officer class. It seems like something that could be pretty fun to play out in a setting. Plus, out of every race in DnD (besides Giffs), an automaton-like race of lawful beings would be the ones that have some technological advances like musketry and bayonets instead.

    Of course, you can take this insanely far and have a Modron army that is commandeered and re-programmed to believe an Illithid Elder Brain is a Hextron who not only has an entire army at its disposal, but also can potentially hide itself from Gith as the Modrons are simply chalked up to invading another plane with the purpose of removing chaos and instilling law and order.

    I have spent way too much time thinking on this.

    1. I certainly think that Modrons will take a Napoleonic view in terms of formations, though arms might depend on the actual availability that you want gunpowder to have in your world.

      I can’t see modrons walking around in the unorganized manner that a lot of PCs do, instead forming exact columns and battle lines, even if cover is available, with Modrons without other orders probably just advancing straight through whatever the PCs throw at them like a Civil war advance straight into enemy fire.

  8. The monodrones actually can’t throw javelins from the air, according to this article , which claims that “flying and attacking would be performing two tasks at a time, which a monodrone can’t do”. To make up for this, I recommend something I had a group of rouge modrons serving a devil army do: Make the monodrones fly the duodrones and tridrones around to chuck javelins from the air!

  9. The startlingly low CR of Modrons did catch my eye, and the question of how they would be encountered at a time/level when they would be any kind of threat quickly followed.
    Then I read the Slaadi text.
    Then I read the Sphinx test.
    Then I schemed.

    I have a level 4 party who need research answers and magic-item-pieces locations, and who are already heading towards a big library.
    So I thought:
    The guardian sphinx will be excited that such a large party has come to see her. She’ll begin changing the floor and surroundings of her lair to be a large Dragonchess board, explaining the SUPER over complicated rules of how to play; making the players roll their eyes, and quite nervous.

    Then the sphinx will stop mid-sentence, the room will snap back to what it had been, and she will say instead that “We are needed. Our converged meetings are fortunate, for the order of the Planes is in danger.”
    The surrounding walls will again begin changing (the Plane shift ability), and the party will arrive on Machanus; on a slowly revolving clockwork hill, with the Grand Clockwork cathedral in sight.

    The Sphinx will be explaining that these beings of complete Law and Order take a mass pilgrimage around the Planes every 289 years, and that the next one is very imminent.
    However, she has senses the chaotic, untimely, surprise arrival of several Slaadi, the Modrons arch-enemies. “This is not a fight between good and evil, to be clear”, she’ll say. “But as fast and free as you all may play with the rules and social constructs on the material plane, I believe none of you can deny how pleasant it is for the Sun to rise each morning, and for gravity to keep pulling you down to the ground. Well if Chaos gets too strong of a foothold – and this surprise attack shows increased boldness and ingenuity on the part of Chaos’ main agents – then those simple things may not forever be dependable.”

    And so, I will avoid the riddle-me-this trope for the Sphinx encounter, I’ll get some low level planes travel, some quirky beings, and some ravenous, deadly things to bash and dominate, all at the same time.

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