Daily Monster #52: Rust Monster

Is your paladin getting too cocky? Are you tired of your cleric/sorcerer casting Shield of Faith AND Shield for an AC of 27? Boy we got something for you today…

Today we’re going to be taking a look at another one of those monsters that have been a part of the world of Dungeons and Dragons for a very long like. Tired of never hitting the fighter and the cleric? Why not try the…


Rust Monster

The basics

As far as stats go, these creatures are fairly straight forward. Rust Monsters have a very average stat array with +1s to most stats except for CHA and INT, which are a -2 and -4 respectively.

Likewise, they don’t really get much in the way of languages or saves, or anything like that. The only perk they enjoy is having a Darkvision of 60ft, which, I suppose is better than what some playable races get.

“I-I don’t wanna talk about it.”

These creatures are considered medium monstrosities and are usually unaligned. They have an AC of 14, a slightly above average movement speed of 40ft, and a hit point pool of 5d8+5.

What makes these creatures interesting is their affinity (or lack thereof) with metals. In fact, the Rust Monster is able to smell the location of any metals within 30ft of it.

Yeah, even that thing that the rogue stole from that town two sessions ago.

I imagine this next feature doesn’t come as a surprise either but, thanks to their Rust Metal feature, any non-magical weapon that manages to land a hit on this creature suffers permanent damage to the point where it can end up being destroyed. Likewise, our Rust Monster can take its action to use its Antennae to corrode metal objects within 5ft on a failed DEX save. Unfortunately for the heavy armored adventurers, this definitely includes armor and shields, which, similarly to weapons, take permanent damage on a fail save and can also be completely destroyed.

Other than making the righteous Paladin quake in their boots at the prospect of losing their favorite sword these creatures don’t get much else; their only output for actual damage is a single Bite attack that does as much damage as you’d expect for a CR 1/2 creature.

The lore

In the world of Dungeons and Dragons, a big majority of the monsters that we stumble upon as in fact versions of creatures detailed in the various mythologies of the world. The Rust Monster, however, isn’t one of them. Although it has been a part of the game for all of its iterations, we can at most speculate that they were the result of taking inspiration from a box of children’s toys.

But what do we know for certain about these creatures? Well, for starters they’re giant bug like monsters roughly about the size of a pony, with chitinous armor and two antennae that grow from the sides of their heads. These are the most important feature of a Rust Monster and what allows that very particular ability to turn the strongest of metals into a pile of mush. It’s not only the antennae that have a rusting property; it’s a very specific combination of bacteria in their blood, which is also the reason why cutting into these things doesn’t bode well for metal weapons.

Rust Monsters are, for the most part, extremely docile creatures that will not attack anyone who isn’t carrying metal. In fact, even if you are carrying metal, it is likely that they would simply ignore you and go straight for the metallic item instead.

Since these creatures prefer to inhabit underground areas, it’s not unlikely to come across them while in a mine shaft. This is one of the reasons why dwarves and other mining races have developed ingenious traps and systems to maintain the Rust Monster population on the lower side of things.

Thanks to their mostly non-aggressive natures, it’s not unheard of for individuals to use them in the disposal of old metal items and similar tasks. Races like the Kobold have even learned how to use them as mounts to ride into battle and, unfortunately for the Rust Monster, their antennae are crucial ingredients in the making of various magical items.

The execution

There’s a few ways to go about this one, the first is to simply have the party be tasked with harvesting a number of antennae for the creation of a magical item, whether that be the cost of creating an item of their choosing or simply a quest from an NPC that’s up to you. I’ve done this for my Ghost of Saltmarsh campaign on several occasions and it always turns out pretty well.

Another alternative is to have the group learn about (or run into) a convoy of miners that urgently need the party’s assistance in dealing with this creature. Hells, we even have a module with the word “mine” in it so this encounter should be easy enough to set up. Just for the heck of it, we could even have this be a rescue mission; maybe one of the least experienced miners found themselves terrified at the sight of these creatures, panickedly ran, and climbed up a pillar or something.

This is exactly what miners look like where I’m from.

Depending on how prepared you want your players to be for this one, they could have little information about the “strange bug creatures” that are harassing the miners. Remember that, if the wizard rolls a good history check to recall information about these creatures or if the miners simply supplies the party with information, it is likely that this encounter wouldn’t turn to combat at all, but rather become a game of persuading the trapped individual into calming down and relinquishing their metal tools.

In terms of combat, it’s important to remember that these creatures won’t actually use their bite attacks unless cornered and extremely hurt and that they will simply try to get at the biggest source of metal that they can find. Rust Monsters might not be exactly a lethal encounter, but they are certain to test your players’ mettle.


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