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Mimic, Rust

Family: Mimic

Medium monstrosity (shapechanger), neutral

Armor Class 14 (natural armor)
Hit Points 67 (9d8 +27)
Speed 15 ft.

18 (+4) 12 (+1) 17 (+3) 6 (-2) 13 (+1) 8 (-1)

Skills Perception +5, Performance +2, Stealth +3
Damage Immunities acid
Condition Immunities prone
Senses darkvision 60 ft., passive Perception 11
Challenge 4 (1,100 XP)


  • Shapechanger. The rust mimic can use its action to polymorph into an object or back into its true, amorphous form. Its statistics are the same in each form. Any equipment it is wearing, carrying, or stuck to it isn’t transformed. It reverts to its true form if it reaches 0 hit points.
  • Adhesive (Object Form Only). The rust mimic adheres to anything that touches it. A Huge or smaller creature adhered to the rust mimic is automatically grappled by it (escape DC 14). Ability checks to escape this kind of grapple are always made at disadvantage.
  • Grappler. The rust mimic has advantage on attack rolls against any creature grappled by it.
  • Specific False Appearance (Object Form Only). While the rust mimic remains motionless, it is indistinguishable from an ordinary object. Due to their specified dietary needs, rust mimics only shapechange into objects that serve as good lures to sate them. This means they often turn into weapon racks (weapons), armor mannequins (armor), heavily locked chests (lockpicks and treasure), and anvils (forge tools and materials) are all commonplace lure shapes.
  • Corrosive. Nonmagical metallic objects that contact a rust mimic for more than a few seconds begin to corrode. This includes weapons that strike it. After dealing damage (if an attack), the metallic weapon takes a permanent and cumulative -1 penalty to damage rolls. In the case of non-weapon items, they suffer -20% of their hit points automatically per round of contact. If a weapon is reduced by -5 damage permanently or another object loses 100% of its hit points, it is corroded to flakes of rust and tarnish beyond nonmagical repair. For some odd alchemical reason, the metal electrum is completely immune to this trait.


  • Corrosive Pseudopod. Melee Weapon Attack: +6 to hit, reach 5 ft., one target. Hit: 8 (1d8 +4) bludgeoning damage. If the rust mimic is in object form, the target is subjected to its Adhesive and Corrosive traits.
  • Toxic Bite. Melee Weapon Attack: +6 to hit, reach 5 ft., one target. Hit: 8 (1d8 +4) piercing damage plus 4 (1d8) acid damage. The rust mimic’s teeth are always made up of half-corroded, jagged metal shards made from their meals, forcing a Dexterity saving throw DC 12 or become poisoned for the next 1d6 hours.


Surprise Round-Most encounters start with the shapechanged creature exploding outward from its hiding place-but not until it has taken a few rounds to corrode and absorb a rogue’s thieves’ tools or a warrior’s prized dagger or helmet. Once it has a solid snack, a meatier meal is welcome.

Adhered Round-Once a rust mimic is grappled to a target, it will continue to try and maneuver itself around that target’s body to corrode as much worn metal as the target has, all the while biting chunks from it. These bites are toxic, and once its foul tarnish infests its target, it becomes even more difficult to be free of the sticky, malleable monster. Although capable of creating pseudopods to strike at non-grappled targets, rust mimics will normally maintain attacking a single target until it is fully incapacitated before moving on.

Hidden Round(s)-Rust mimics are not mindless beasts, and if injured badly, they will slink away to hide, shapechange, and heal. Once fully healed, the rust mimic will resume its normal hunting position and lure form.


Mimics have plagued weary travelers and adventuring types for the span of written history, but only in recent decades have scholars begun to recognize some individual subtypes of the shapechanger appearing with some regularity. One of these subspecies called a rust mimic due to the special properties of their secretions. They are noted easily by their predilection toward particular objects to transform into a perfect trap to lure in targets who use things made from their most delectable dietary supplement-metal.

Mimics use their shapechanging abilities to draw in prey by looking like objects that attract animals and adventurers to their awaiting, sticky pseudopods. Rust mimics take an extra step in their predatory shifting by choosing objects most likely to be touched or interacted with by common metallic objects, like locks, anvils, or toolshed racks.

Mimics of all kinds, while monstrous horrors in their own right, survive by consuming creatures drawn into striking range and then consumed. Unlike the rest of their cousins, they have evolved to require special additives to their diet-metal. The metals it eats are then used to strengthen and grow certain aspects of the creature, especially its jagged, rusted fangs. Yet to be explained by researchers, rust mimics cannot digest or corrode the semi-precious metal electrum; it is as if it almost has an allergy to the stuff.

d4 Rust Mimic Treasure
1 potion of hill giant strength
2 4d20 gp
3 arrow of slaying
4 arcane focus (GMs choice)
Section 15: Copyright Notice

Book of Monstrous Might (C) 2021 Total Party Kill Games. Author(s): Brian Berg, Mark A. Hart & Danny Grimes.

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