Rust Monster Larva, Hatchling

Medium monstrosity, unaligned

Armor Class 14 (natural armor)
Hit Points 16 (3d8 + 3)
Speed 30 ft.

13 (+1) 12 (+1) 13 (+1) 2 (-4) 13 (+1) 6 (-2)

Skills Perception +1
Senses darkvision 60 ft., passive Perception 11
Challenge ½ (100 XP)


  • Iron Scent. The rust monster can pinpoint, by scent, the location of ferrous metal within 30 feet of it.
  • Rust Metal. Any nonmagical weapon made of metal that hits the rust monster corrodes. After dealing damage, the weapon takes a permanent and cumulative -1 penalty to damage rolls. If its penalty drops to -5, the weapon is destroyed. Nonmagical ammunition made of metal that hits the rust monster is destroyed after dealing damage.


  • Bite. Melee Weapon Attack: +3 to hit, reach 5 ft., one target. Hit: 5 (1d8 + 1) piercing damage.
  • Antennae. The rust monster corrodes a nonmagical ferrous metal object it can see within 5 feet of it. If the object isn’t being worn or carried, the touch destroys a 1-foot cube of it. If the object is being worn or carried by a creature, the creature can make a DC 11 Dexterity saving throw to avoid the rust monster’s touch. If the object touched is either metal armor or a metal shield being worn or carried, it takes a permanent and cumulative -1 penalty to the AC it offers. Armor reduced to an AC of 10 or a shield that drops to a +0 bonus is destroyed. If the object touched is a held metal weapon, it rusts as described in the Rust Metal trait.


From the clutches of heavy iron eggs, rust monster larva spawn. Though they start as worm-like creatures, they quickly grow into fully formed, but smaller versions of their adult selves — rust colored insectile creatures, whose antenna can sense metal and whose mandibled bite can devour even the hardest steel. It takes them many years to grow, molting flakes of rust and shedding an exoskeleton of brittle iron. The more metal they consume the faster they mature. They will eat nearly any metal, but savor ferrous metals such as iron and steel best of all.

Adventurer’s Pests. Rust monster Larva are often encountered close to human, dwarvish, and gnomish civilizations, where iron is most abundant. They thrive in places where such metal has been abandoned; collapsed dwarven halls where ancient battles were fought, abandoned gnomish workshops, or human foundries in their sprawling cities. Rust monsters are mostly considered pests at best, and dangerous threats at worst. Sentient races often hunt them to extinction, forcing them back to the edges of their civilizations.

Practical Corrosion. Some factions have been known to breed and train rust monsters. Thieves guilds will sometimes use them for break ins, to gnaw through prison bars or chew through the door of a vault. In warfare, they are sometimes employed in harrying the enemy, packs are unleashed on the enemies camps, devouring their armory and supply caches before they can be driven off. It is said that the scales of a fully grown rust monster can be melted down and forged into magical blades that rust any weapons or armor they strike.

Section 15: Copyright Notice

Zargoth’s Tome of Familiars, Copyright 2021, Arcana Games, LLC.

Section 15: Copyright Notice

Zargoth’s Tome of Familiars, Copyright 2021, Arcana Games, LLC.

This is not the complete section 15 entry - see the full license for this page