Living Steel

This gleaming, almost fluid humanoid of steel reflects light and absorbs heat, appearing as a cold blue shape to infravision. It is seldom the aggressor, but once provoked it pursues a foe until one of them dies.

Weapons below +2 pass harmlessly through it, the metal simply closing behind them and only annoy it. Its real strength is shapechanging: it can become a racing steel hound, a man with swords for forearms, or nearly anything else of the same mass. It cannot change color, it gains the speed of a new shape but none of its special abilities (no flight, keen nose, poison or magic resistance), and it cannot grow or shrink, so a dragon or a mosquito is beyond it. It can, however, flow through narrow cracks.

Changing shape takes a full round, during which it cannot attack or defend, drops to AC 5 and can be harmed by normal weapons, so it rarely does so mid-fight.

Fire and electricity are harmless unless a single attack deals more than 55 points of damage. Lesser fire actually melts it into a state where it can reshape and attack in the same round. Above 55, it takes full damage and spends two rounds gathering its scattered pieces. Cold is its weakness: it drops to movement 6 with one attack, needs two rounds to change form, and for two rounds after a cold attack lands, its foes deal double damage and even unenchanted weapons can hurt it.

Strictly solitary, living steel reproduces without a mate. Two that meet fight to the death, usually won by the one with the cleverest and deadliest shapes, and the victor absorbs the loser's mass. It dens in rock crevices reachable only by thin cracks, where it relaxes into a shapeless blob.

It must eat iron and lives near ore veins or other rich iron sources. Most of what it eats fuels its movement, but each night it sheds a small refined portion in its lair. With daily access to ore, that mass becomes a new, sentient living steel after one year.