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| Art from Dungeon of the Mad Mage, property of WotC |
The origin of rust monsters is unknown, but multiple theories have arisen over time. The vast majority of these see these creatures as a form of curse or punishment on civilisation, degrading and feeding on the tools that separate them from wild beasts. Whether their creators are malicious and spiteful gods or malicious and spiteful mages is yet to be determined.
Rust monsters have slow metabolisms and are opportunistic feeders. The ravenous individuals located in dungeons are hungry and malnourished, having picked clean the iron and steel within, then gone into a state of hibernation until more food presents itself. Those found deeper underground, where metal deposits are easier to reach, are typically more docile than their overground counterparts. This does little to raise the spirits of the miners who have to deal with rust monsters feeding on the deposits they're trying to harvest.
If you find yourself traversing a dungeon with no locks on doors or bars on prison cells, be on your guard. Abandoned buildings from iron-age periods are a popular feeding ground for rust monsters. Villagers may inform you of a simple trick to avoid rust monsters: throw iron coins at them to distract the creatures as you flee. Do not do this. If you are curious to see why this is bad advice, try throwing some meat on the ground for a hungry dog and see if it will leave you alone afterwards.
Historian Guilds across the lands lament for the fragments of the past lost to their appetites. In regions where rust monsters were common, there is an increase in tool creation from non-ferrous materials; this also coincides with the amount of historic records present from bronze and brass age civilisations when compared to iron and steel age societies.
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| Amphipods make good visual references for rust monsters. Photo by Katrine Kongshavn. |
Regional variants of rust monsters possess different abilities. Some are mildly magnetic (advantage on attack rolls against targets in medium or heavy metal armour), with a few being so magnetically charged that weapons stick to their shells (akin to the kuo-toa's sticky shield trait). Others are more adapted to sneaking up on unsuspecting meals, with abilities such as standing leap or nimble escape. Some adventurers have reported finding cave-dwelling variants able to squeeze through narrow gaps and reach further than their cousins, allowing them to get at iron deposits deeper within the earth.
The antennae of rust monsters can be made into weapons that possess similar properties, albeit for a limited period of time. They are especially favoured by thieves and saboteurs, as well as those frequently fight enemies in plate mail. Their limited longevity means that rust monsters must be harvested regularly in order to keep a ready supply; the severing of their antennae ensures the likely death of the creature, as it no longer is able to turn metals into rust, yet alone detect ferrous metals nearby.
Rust Blade/WhipWeapon (dagger or whip), uncommon
This item is clearly made from the antennae of a rust monster, with a handle made of treated wood or bone. The weapon has the same properties as its mundane counterpart. If a target is wearing nonmagical metal armour on a successful hit, their armour class is reduced by -1. If it is reduced by -5, the armour is destroyed. If the attack roll is a natural 1, the rust blade or whip is broken and cannot be used as a weapon.
This item maintains its properties for 30 days. After this time has passed, the antennae loses its rusting ability and becomes brittle, disintegrating upon its next successful hit.
Attempts have been made to create Rust Armour, with the hopes of having the same weapon-degrading properties as the creature's exoskeleton. Attempts so far have been unsuccessful, with the plates flaking apart over time, as well as testers complaining about the fact that they are still injured each time the weapon makes contact with their armour.
Rust monster eggs can also be effective tools in warfare and sabotage. Individuals able to get them into an enemy's armoury or fortifications can cause the enemy to disintegrate from the inside out as the rust monster hatchlings chew through their weapon stores.
