This massive wormlike creature of burnt iron and glistening hematite grinds with the roar of the forge. Its fanged lamprey like mouth opens to reveal the molten fires burning in its gut.
Slag Worm CR 20
XP 307,200
N Gargantuan outsider (earth, elemental, extraplanar, fire)
Init +2; Senses darkvision 60 ft., tremorsense 60 ft.; Perception +35; Aura intense heat (10 ft., DC 30, 4d6 fire)
Environment any (Elemental Planes of Earth, Elemental Planes of Fire, Plane of Molten Skies)
Organization solitary
Treasure none
Slag worms burrow endlessly through the elemental Plane of Earth, Elemental Planes of Fire, and Plane of Molten Skies, occasionally forcing through weak points into the material planes where they burrow deep beneath the earth, devouring raw iron deposits to keep their internal furnaces burning. Because of this they have been known to devour entire companies of heavily armored dwarves and orcs, mistaking their gear for a new vein of naturally occurring iron salts.
Slag worms average about 40 feet long and weigh about 60,000 pounds, though specimens as large as 100 feet or more have been rumored to exist. Its massive form radiates abysmal heat and when the worm opens its maw, fires can be seen burning and raging in its interior. They are intelligent creatures (more so than their appearance of a big dumb worm would lead one to believe) and can speak though they rarely choose to converse with other races.
A slag worm erupts from the ground seeking to eat anything wearing iron, steel, or other metal armor or equipment. It attacks such creatures with a great ferocity, generally disregarding other enemies until the worm is heavily injured or forced away by magic.
Slag Worm from the Tome of Horrors Complete, Copyright 2011, Necromancer Games, Inc., published and distributed by Frog God Games; Author Scott Greene.