I am about to run an encounter of the week featuring modrons that includes combat encounters with monodrones and duodrones.

The stats for modrons state:

Cogs of the Great Machine. If a modron is destroyed, its remains disintegrate. A replacement from the next lowest rank then transforms in a flash of light, gaining the physical form of its new rank. The promoted modron is replaced by one of its underlings in the same manner, all the way to the lowest levels of the hierarchy.

Canonically, what is the mechanism that decides modron promotion? Would the physically closest modron (in the combat) be promoted? Would it be random? Would the promoted modron be on the same plane? Would it be Mechanus?

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    \$\begingroup\$ Promoting the nearest makes for a potentially interesting encounter as taking out the 'boss' first just makes another 'boss'. \$\endgroup\$
    – SeriousBri
    Jun 4, 2020 at 12:01

2 Answers 2


Since this is a lore question, here is an answer from 2e Planescape boxed set Monstrous Supplement (page 18):

Promotion occurs seemingly by accident. As soon as a vacancy occurs, the nearest modron of the next lowest rank is recruited to ascend. Since they have no individuality, there’s no point in trying to promote the “best and the brightest”; all modrons of a given rank are deemed equal.

This information is also referred to in the Mechanus chapter of Planes of Law (page 13), where it is hypothesised that modrons might have a hive mind (a la the Borg). In that scenario, it would be reasonable that the promotion happens in a way that is most beneficial to the hive.

All these are supported by the description in the 5e Monster Manual, which states:

Modrons have no sense of self beyond what is necessary to fulfill their duties. They exist as a unified collective, divided by ranks, yet they always refer to themselves collectively.To a modron, there is no "I," but only "we" or "us."

  • \$\begingroup\$ "promotion happens in a way that is most beneficial" In terms of preservation, it makes sense that if a higher modron is destroyed they're likely to need help or be in a situation that would destroy a lower modron, so it be better for all modrons to have the promotion occur there to help preserve other modrons. \$\endgroup\$
    – StuperUser
    Jun 4, 2020 at 15:17
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    \$\begingroup\$ so players should attack lower rank moedrons first ? Are they healed when they are promoted too ? \$\endgroup\$
    – Orsu
    Jun 4, 2020 at 19:48
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    \$\begingroup\$ We don't know if they are healed when they are promoted. Regardless, it indeed looks like a better strategy to get rid of the lower rank modrons. :-) \$\endgroup\$
    – ZwiQ
    Jun 4, 2020 at 21:08
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    \$\begingroup\$ @StuperUser It might make sense to promote more than one modron - but Modrons sometimes take their "perfect order" to the point of stupidity, and Primus the One has declared that the number of modrons of each rank is fixed: If exactly one modron of rank N is destroyed or promoted, exactly one modron of rank N-1 will be promoted to replace it; no more, no less. \$\endgroup\$
    – GMJoe
    Feb 4 at 23:01

The 2nd ed 'Manual of the Planes Web Enhancement' includes:

Individual promotions occur seemingly by accident. Since modrons have no individuality, there’s no point in trying to promote the 'best and the brightest' — all modrons of a given rank are equal. Thus, the nearest one of an appropriate rank is promoted when a vacancy occurs."

I am interested in what happens to the monodrone gap that is eventually created by the chain of promotions.

'Manual of the Planes Web Enhancement' :

Monodrones, having no castes below them, reproduce by fission to replace lost members.

So it looks like when a monodrone is killed or promoted, a nearby monodrone splits into two monodrones but that is contradicted by the Planescape book "The Great Modron March" :

When a modron dies, it disappears. Some have described the process as rapid decomposition or corrosion, but in the end the modron corpse simply vanishes within seconds. Its essence reverts to Mechanus instantly, where it forms into a new monodrone. If a modron of a higher rank than a monodrone dies, a modron from the rank immediately below is 'promoted'. Then one from the rank below that fills in the void created by the promoted modron, and so on.


Despite some reports, modrons do not reproduce by 'splitting'.

The TGMM explanation makes practical sense as otherwise the army would just keep regenerating - any remaining monodrones could keep splitting into replacement monodrones.


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