Rustrun

"Eugh, this place smells terrible. Almost like...."
"Like what?
"Oh gods. Turn around, go back. There's a rustrun in here somewhere."
"SLORP."
"Nevermind, it's here now."

— Adventurers

 

Okay, who didn't clean their blade?

  The bane of all things metallic, a creeping menace that leaves ruin in its wake. These oozes are dull red-brown, their viscous bodies streaked with rivulets of orange and black, like veins of rust threading through damp iron. Slow-moving but inexorably persistent, a rustrun emits a faint, acrid smell, akin to iron left too long in brackish water. This odour precedes its arrival, a harbinger for those wise enough to notice.   It is said that rustruns are born from the decay of forgotten battlefields, where swords and shields are left to rot beneath the elements. Whether this is true or not, their affinity for corroded metal is unmistakable. They are most often found in the depths of abandoned forges, ancient armouries, or the remains of sieged castles. They cling to walls and ceilings, waiting with deceptive patience for an unwary adventurer to pass below.   A rustrun's touch spells doom for metal. Steel withers into brittle flakes, chains disintegrate, and even enchanted weapons eventually falter against its relentless hunger. Weapons and armour that come into contact with a rustrun are quickly corroded, reducing their efficacy with every passing moment. Curiously, rustruns show no interest in gold, silver, or other “soft” metals, which has led scholars to speculate on the exact nature of their diet. Some claim they are remnants of ancient magical experiments designed to cleanse iron deposits, while others believe they are the cursed spawn of alchemical waste left to fester for millennia.  

Sorry for blaming you, Dennis

  Yet, rustruns are not merely destroyers of metal. They possess a strange, alien cunning, evading wooden or stone weapons with surprising dexterity. Some whisper that these oozes hold the memories of the metal they consume, though none have ever proven it. Mages who study such creatures claim that the faint shimmer of sparks seen within a rustrun's core may be remnants of the life once bound to a blade or shield.   Their danger is compounded by their resilience. Rustruns are immune to most physical attacks, absorbing the force with a wet, slurping sound. Fire slows them but does not kill them, while cold merely causes them to shatter and reform. Acid, ironically, has no effect at all. Adventurers are advised to seek magical solutions, as spells seem to be the only reliable means of halting these creatures.   Worse still, rustruns often travel in loose, drifting colonies, their gelatinous masses blending together until what appears to be one creature is, in fact, many. It is not uncommon for a small group to emerge from an encounter with a rustrun, only to find their retreat blocked by another.