N Medium Aberration
Senses Perception +8; darkvision, metal scent 30 feet
Skills Athletics +7 (+13 to Disarm a metal item)
Str +0, Dex +3, Con +1, Int -4, Wis +1, Cha +0
Metal Scent A rust monster can smell metal as a precise sense.
AC 19; Fort +8, Ref +10, Will +6
Tail Trip Trigger A creature carrying a metal item attempts to move out of a square within reach of the rust monster's tail. Effect The rust monster makes a tail Strike against the triggering creature.
Speed 35 feet, climb 10 feet
Melee antenna +10 (finesse), Effect rust
Melee mandibles +8 (finesse), Damage 1d10+4 piercing
Melee tail +8 (finesse), Damage 1d4+2 bludgeoning plus Improved Knockdown
Antenna Disarm The rust monster attempts to Disarm a metal item a creature is holding using its antenna (with the same modifier as an antenna Strike). On a success, the item is subject to the rust monster's rust ability (see below) in addition to the effects of the Disarm, and if the check to Disarm is a critical success, the rust monster drops the item on the ground in its own space.
Rust A rust monster's antenna causes metal to rapidly rust and corrode. If it succeeds at an antenna Strike or Disarm attempt with its antenna, the rust monster deals 2d6 damage (doubled on a critical hit) to a metal item the target is wearing or holding, ignoring its Hardness. If the rust monster hits an unattended metal item, the item takes this damage automatically. If a creature uses the Shield Block reaction with a metal shield against an antenna attack, the shield is automatically broken, but no other item is rusted on that attack.
Found in lost dungeons, deep caves, and abandoned mines, rust monsters are a bane to any adventurers who rely on armor, weapons, or other metal items.
These strange-looking creatures grow to about 5 feet long, with four insectile legs and a long tail ending in a four-pronged appendage resembling a tiny windmill.
However, it is the rust monster's feathery antennae that strike fear in the hearts of battle-hardened warriors, for a single touch from even just one antenna can reduce an adventurer's most valuable tools to a useless pile of rust.
Rust monsters aren't inherently aggressive creatures, but they're voracious oxidivores, meaning they consume the rust created by their antennae. The creatures savagely attack anything that gets between them and a possible meal, and they relentlessly pursue any source of metal. A rust monster can be distracted by a single metal-rich item, but they are often encountered in groups of three or more, sharply raising the cost of escape.
Rust monsters are a terrible scourge in mining communities. If a group of rust monsters discovers rich veins of ore, they can multiply quickly. By weakening tunnels, attacking workers, and consuming the source of the miners' livelihood, these aberrations have created many mountainside ghost towns.