Starfinder: Evolved Rust Monster

Chris Van Deelen

Rust monster, Evolved Combatant CR 5 XP 1,200

Neutral medium aberration

Init +5; Senses: Darkvision 120 ft., sense substance 500 ft.; Perception +11


Defense                                                             HP 70

EAC: varies; KAC: varies

Fort: +7; Ref: +7; Will: +6

Defensive Abilities: Specialized resistances; Immunities: Cold, radiation, vacuum.



Speed: 40 ft.

Melee: Two tentacles +10 (1d6+8 B)

Space: 5 ft., Reach: 5 ft.

Offensive Abilities: Destroy substance



Str +3; Dex +5; Con +3; Int -3; Wis +0; Cha +0

Skills: athletics +16, survival +11

Other Abilities: Free traveller, hibernation

Languages: None



Environment: Any

Organization: Solitary, pair, small group (1d4+2), search and destroy pack (2d6+4)


Special Abilities

Destroy substance (Ex): Depending on the species, the evolved rust monster can affect different types of compounds. Nearly all armor, weapons and equipment often employ varying compounds, such as plastics, polymers, metals, ceramics and the like. As such, when the creature attacks, it will attempt to touch an item. If the attack roll succeeds, the tentacle will cause the item to corrode and often fall apart. The item is allowed a Ref save (using the wielder’s save) against DC 17. If it fails, the item is destroyed. If the technological item in question has many different components and different substances, if the save fails, use the following chart to see what happens. Note the damage effects are cumulative, so it would not take long to destroy an item.


Destroy Substance Table




Minuscule damage – item works normally. Takes 1 point of damage.


Minor damage – If a ranged weapon, suffer a -2 to hit and -1 per dice damage. Armor loses -2 to both AC types, other technological item will malfunction 20% of the time. Loses 25% of its total hit points.


Major damage – If a ranged weapon, suffer a -4 to hit and -2 per dice damage. Armor loses -4 to both AC types, other technological item will malfunction 50% of the time. Loses 50% of its total hit points.


Catastrophic damage If a ranged weapon, suffer a -6 to hit and inflicts only half the normal damage. Armor loses -6 to both AC types, other technological item will malfunction 80% of the time. Loses 75% of its total hit points.


Destroyed. Time to get some new toys.


Free Traveller (Ex): All members of this species possess the ability to cling to any surface, giving them normal movement rate, and are able to use tiny puffs of internal gases to move freely in space. This allows them normal movement while in vacuum.

Hibernation (Ex): The creatures can enter a state of hibernation, which is very useful when they are in the depths of space. They can remain this way indefinitely, which can theoretically allow them to travel interstellar space, but it would take millennium to travel even to the nearest star system. This is very useful for the creatures as they travel from asteroid belt to asteroid belt or wait (after being seeded) for a hapless ship to ‘bump’ into.

Sense Substance (Ex): The creature is able to sense the substance it uses as food up to 500 feet from its location.

Specialized Resistance (Ex): Thanks to the specific type of material the creature can destroy and incorporate into its body, the various sub-species have additional resistances. See the sub-species chart for the type of resistances it possesses.


Sub-species Table




Specialized Resistance





DR 10 / Slash or Pierce





DR 10 / Slash or Pierce, Energy Resistance 5 / all





Electrical resistance 10

Marbled typically grey / white

Plastic / Rubber



Acid resistance 10

Bluish black




Fire resistance 10


Ultra-dense Material



DR 15 / -



Many worlds were plagued by these strange aberrations, as their appetite for metals was all but insatiable. Many warriors would flee in terror at the hint of these strange creatures. Even magical weapon was not immune to the voracious appetite of these monsters, although such devices typically lasted longer than mundane items.

As technology began to take hold on many worlds, these creatures became more of a threat – they could disable or destroy vehicles, damage structures, or even consume entire mines filled with metal that was needed for the burgeoning industrial complex.

The result is many of the worlds hunted these creatures to extinction. Others set aside special areas where they could live in peace, being fed scraps in order to keep them hale and healthy.

And of course – there were those who decided to modify these creatures through the use of magic or genetic engineering. The end result is these creatures went from being a nuisance (or terror, depending on who you asked), to an outright deadly foe. Some nefarious governments even used these as front-line combatants when dealing with powered armored foes.

Of course this worked for a time, until modern technology allowed for the creation of ceramic and polymers, which often had the same strength and durability of many old alloys and metals, but were typically lighter in weight.

For a while, the tactic using these creatures to engage and destroy enemy armor and weapons made of simple metal worked, and then they ran into the new technology. The attacks still were somewhat effective, causing some damage and the occasional malfunction, but for the most part, the enemy just destroyed the aberrations with little effort.

Going back to the drawing board, the geneticists modified these creatures so that they could consume polymers, ceramics, plastics and other such material. This resulted in the creation of several sub-species of the Rust monster, and once again they had the advantage in the war.

One of the changes that were made with these creatures is that they would absorb the materials they destroyed, and incorporate them into their flesh. The creature’s flesh would often have the consistency of metal, making it very difficult to harm using conventional or physical weapons. The best way to deal with the creature is to use energy and long-ranged attacks.

If the change in diet and addition of incorporating the meals into its body, they could also use the material to store energy, which they could use to survive in vacuum. As long as they had material to consume, they could survive in the depths of space indefinitely. As such, many militaries would ‘seed’ asteroid belts or even commonly used shipping or travel lanes with these creatures, waiting for some hapless ship to literally stumble upon them. Living mines.

Often packs of these creatures are made up of several different types of sub-species. These creatures work together as a single unit, deploying their unique appetites to break through the hulls of starships, where they can enter and create havoc. Typically these creatures will inflict damage on a ship, usually only 1d4 points per creature, per hour, but they have a bad habit of causing cascading effects. In other words, once an hour the ship has a 10% chance per creature on board to suffer specific system damage. So if a ship has 10 of these creatures wreaking damage and chaos, then there is a 50% chance a random system will suffer damage.

When combating Androids, Drones or Constructs (robots, golems, etc.), combat is a little different. Although living entities, Androids still use artificial components, and as such nearly all types of Evolved rust monsters are able to hurt them in one manner or another. Each time an android is hit in combat, it must make a Fort save DC 13 or take 1d3 points of temporary Constitution damage, as the creature destroys and consumes vital parts of its structure.

Constructs, drones, robots and other such constructs take more damage from these attacks. They suffer 4d6+8 B damage, and will also suffer Constitution damage. A critical hit against such a target uses the standard wound table, with one exception – the Brain results in instant death of the target, not stunned for 1 round.

Starfinder Creature Index

Chris Van Deelen is the creator and contributor to over half of the Wisdom from the Wastelands series, contributor to the Swords of Kos: Hekaton anthology, and the recently released 'Swords of Kos: The Rite'. He also wrote Creatures of the Tropical Wastelands, and 100 Oddities found in a Car. As prolific as he is, Chris Van Deelen continues to write and produce material which will be in publication soon. Not only is he a prolific content creator, he also has a wide selection of fiction and stories! If you like his work, please follow his personal author page on Facebook and on Twitter to keep up with his latest news and game content.