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Rust-Troll: The Armor-Eater’s Horror

A terrifying fusion of regenerating troll-flesh and the metal-dissolving instincts of a rust monster.

Quite some time ago we came up with a terrifying monster concept. As I was looking through those videos I realized I never made a post here with stats. You can check out that video here. You can see even more fun with trolls here.

📖 Lore

The Rust-Troll is a product of alchemical madness or aberrant evolution — a rare fusion of two deeply unnatural creatures: the savage troll and the insatiable rust monster. Most scholars agree this combination should not exist. And yet, somewhere deep in the bowels of cursed dungeons or mad wizard laboratories, it does.

Long tendrils sprout from the creature’s back and shoulders, twitching with predatory awareness. These rust-coated feelers pulse with acidic ichor, corroding anything metallic they touch. The troll’s traditional regeneration is intact — but twisted. When it consumes oxidized metal, its regeneration accelerates, causing bone and sinew to erupt unnaturally and mend in grotesque ways.

Blacksmiths tell stories of rust-trolls skulking near forges, waiting for the perfect time to strike. Paladins weep at the loss of enchanted plate. And adventurers who rely too heavily on gear quickly learn: you can’t fight what eats your sword.

🧠 Combat Tactics

• Gear-Destroyer: The rust-troll prioritizes heavily armored targets, attempting to disarm or destroy their gear while tanking damage with its regeneration.

• Ambusher: Often lies in wait near metal-rich environments like dwarven ruins, treasure hoards, or blacksmith enclaves.

• Eat to Heal: If severely wounded, it will retreat briefly to consume nearby metal objects and heal rapidly.

💡 Adventure Hooks

• A nearby town’s entire guard has been disarmed — literally. Their weapons dissolved into rust overnight.

• A dwarven citadel has gone silent. Rumors say a “metal rot demon” stalks its adamantine halls.

• An artificer hires the party to retrieve a rare rust-troll gland — a key ingredient in anti-metal warforged armor.

🧬 Rust-Troll

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Large monstrosity, chaotic evil

Armor Class 16 (natural armor)
Hit Points 136 (16d10 + 48)
Speed 30 ft.

Saving Throws Con +6, Wis +3
Skills Perception +3, Survival +3
Damage Resistances bludgeoning, piercing, and slashing from nonmagical attacks
Damage Immunities poison
Condition Immunities poisoned
Senses darkvision 60 ft., passive Perception 13
Languages Giant
Challenge 8 (3,900 XP)
Proficiency Bonus +3

Traits

Regeneration. The rust-troll regains 10 hit points at the start of its turn. If the troll takes acid or fire damage, this trait doesn’t function at the start of its next turn. The rust-troll dies only if it starts its turn with 0 hit points and doesn’t regenerate.

Metal-Eater. As a bonus action, the rust-troll can consume a piece of metal equipment (within 5 feet or grappled). The object must be nonmagical and made of metal. The object is destroyed, and the rust-troll regains 15 hit points.

Corroding Tentacles. The rust-troll’s long feelers count as natural weapons and have the corrosive effect of a rust monster. Any metal armor or weapon struck by its tentacle attack begins to corrode.

Actions

Multiattack. The rust-troll makes two claw attacks and one tentacle attack.

Claw. Melee Weapon Attack: +7 to hit, reach 5 ft., one target.
Hit: 11 (2d6 + 4) slashing damage.

Tentacle. Melee Weapon Attack: +7 to hit, reach 10 ft., one creature or metal object.
Hit: 9 (2d4 + 4) bludgeoning damage. If the target is wearing nonmagical metal armor or wielding a nonmagical metal weapon, it must succeed on a DC 15 Dexterity saving throw or the item takes a permanent -1 penalty to AC or damage rolls. Armor reduced to AC 10 or weapons reduced to 0 damage are destroyed.

Devour Metal (Recharge 5–6). The rust-troll chooses a 10-foot cube area within reach. All unattended metal objects in that area are destroyed if nonmagical. For each object destroyed, the rust-troll regains 5 hit points (to a maximum of 30).

🧪 Variant: Alchemical Rust-Troll

A rare alchemist-enhanced version has metallic plating fused to its hide. This variant has:

• AC 18

• Magnetic Pulse (Recharge 6): All creatures wearing metal armor or holding metal weapons within 20 ft. must succeed on a DC 14 Strength saving throw or be pulled 10 ft. toward the rust-troll and knocked prone.

🧨 DM Tips

• The rust-troll is a gear check and encounter tax rolled into one — but it shouldn’t feel cheap. Telegraphed environments (rusted weapons, corroded walls) give fair warning.

• Allow clever players to trick the rust-troll into consuming cursed or explosive metals.

• Make metal scarcity a plot point. Towns might ban metal-carrying adventurers if a rust-troll is nearby.

Thanks for reading. Until Next Time, Stay Nerdy!!