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Rust Monster

• Size: Medium
• Type: Monstrosity
• Alignment: Unaligned
• AC: 14
• Initiative: +1 (11)
• HP: 33(6d8+6)
• Speed: 40 ft

ATTR	VAL	MOD	SAVE
STR	13	+1	+1
DEX	12	+1	+1
CON	13	+1	+1
INT	2	-4	-4
WIS	13	+1	+1
CHA	6	-2	-2

• Senses: Darkvision 60 ft.; Passive Perception 11
• Languages: None
• CR: 1/2 (XP 100; PB +2)

Traits

Iron Scent. The rust monster can pinpoint the location of ferrous metal within 30 feet of itself.

Actions

Multiattack. The rust monster makes one Bite attack and uses Antennae twice.

Bite. Melee Attack Roll: +3, reach 5 ft. Hit: 5 (1d8+1) Piercing damage.

Antennae. The rust monster targets one nonmagical metal object—armor or a weapon—worn or carried by a creature within 5 feet of itself. Dexterity Saving Throw: DC 11, the creature with the object. Failure: The object takes a -1 penalty to the AC it offers (armor) or to its attack rolls (weapon). Armor is destroyed if the penalty reduces its AC to 10, and a weapon is destroyed if its penalty reaches -5. The penalty can be removed by casting the Mending spell on the armor or weapon.

Destroy Metal. The rust monster touches a nonmagical metal object within 5 feet of itself that isn't being worn or carried. The touch destroys a 1-foot Cube of the object.

Reactions

Reflexive Antennae. Trigger: An attack roll hits the rust monster. Response: The rust monster uses Antennae.

Lore & Background

Rust monsters are bizarre aberrations that feed on metal, possessing the supernatural ability to corrode and consume iron and steel with a simple touch. These armadillo-like creatures are the bane of armored warriors and civilized societies that depend on metal tools and weapons. Their very presence can reduce a knight's full plate armor to worthless rust in moments, making them among the most feared creatures for equipment-dependent adventurers.

Despite their destructive capability, rust monsters are not inherently malicious - they simply follow their biological imperative to seek out and consume metal. They are drawn to areas with high concentrations of worked metal, often following trade routes, besieging settlements, or lurking near battlefields where they can feast on discarded weapons and armor.

Combat Tactics

Rust monsters prioritize destroying metal equipment over directly harming opponents, using their antennae to corrode weapons and armor on contact. They instinctively target the most heavily armored enemies first, as these represent the richest sources of food. Their tactics focus on disarming and unarmoring opponents rather than dealing direct damage.

These creatures use hit-and-run tactics, darting in to touch metal equipment before retreating out of range. They are surprisingly agile and persistent, following opponents who flee until they can access their metal possessions. Against unarmored or lightly equipped foes, rust monsters may lose interest unless directly threatened.

Encounter Ideas

1. The Caravan's Nightmare A rust monster has been following a merchant caravan, systematically destroying metal goods during nighttime raids. The party must protect the remaining valuable cargo while finding a way to deal with the persistent creature without losing their own equipment.

2. The Forge Guardian A rust monster has taken up residence near a blacksmith's workshop, drawn by the constant presence of metal. The creature's proximity threatens to destroy the smith's livelihood, and the party must relocate or eliminate it while protecting valuable tools and finished goods.

3. The Castle's Bane A rust monster has infiltrated a fortress, systematically weakening its defenses by corroding weapons, armor, and structural elements. The garrison becomes increasingly vulnerable to outside threats as their equipment fails, requiring immediate intervention.

4. The Archaeological Disaster Excavation of an ancient site has attracted rust monsters to the metal artifacts being uncovered. The creatures threaten to destroy priceless historical treasures, and the party must balance preservation efforts with creature management.

Environmental Effects

• Metal Corrosion: All metal objects in the area show signs of accelerated aging and rust, even without direct contact
• Equipment Anxiety: Knowledge of rust monster presence makes warriors reluctant to use their best equipment
• Economic Impact: Trade routes and settlements may be abandoned if rust monster activity becomes too frequent
• Technological Regression: Areas with persistent rust monster populations often revert to stone, wood, and bone tools

Treasure

• Metallic Residue (10-50 gp): Valuable mineral concentrates left behind after the creature processes metal
• Rust Monster Antenna (200 gp): Severed antenna retains limited metal-corroding properties for alchemical use
• Non-Metal Valuables (varies): Gems, organic materials, and other treasures the creature cannot consume
• Crystallized Iron (100-400 gp): Rare formations created when the creature's digestive process is interrupted
• Ancient Coins (varies): Pre-corrosion currency made from metals the creature has partially processed

Plot Hooks

1. The Weaponless War Two armies preparing for battle discover rust monsters in the battlefield area. The creatures' presence forces both sides to fight with improvised weapons and non-metal equipment, dramatically changing military tactics and potentially preventing large-scale warfare.

2. The Rust Plague Multiple rust monsters appear in a region simultaneously, suggesting they're being deliberately introduced or bred. The party must investigate the source while helping communities adapt to life without reliable metal tools and weapons.

3. The Living Recycling An eccentric inventor has trained a rust monster to help with metal processing and recycling operations. However, the creature has begun expanding its diet beyond intended materials, threatening the inventor's workshop and nearby community.

4. The Explorer's Dilemma Ancient ruins protected by rust monsters contain treasures that would be destroyed by the creatures' presence. The party must find creative ways to bypass or relocate the monsters while preserving both the artifacts and their own equipment.