Iron Cobra

An iron cobra resembles a real venomous snake, built of tapering metal segments, the biggest about 3 inches long just behind the head. Makers painted them to mimic deadly species like the copperhead or cobra, sometimes adding rattles, forked tongues or hoods. The eyes betray it: two enchanted emeralds worth at least 500 gp apiece. Those made by minor deities copy nature so well that the truth may emerge too late.

Mindless, it ignores charm monster, sleep, hold monster and other mind-affecting magic, and no web sticks to it. Nonmagical weapons do half damage. It hides in shadows 85% of the time, is invisible to infravision because it emits no heat, and saves vs. magic as its creator (usually 12th level or better). Once per turn it can move silently for a round to slip behind a victim.

Its bite deals 1d3 piercing damage and injects a dose from its reservoir. Most hold lethal venom: save vs. poison at -2 or die. Others carry paralytic poison (2-5 rounds), a sleep drug that ignores Hit Dice (1-4 rounds), a hypnotic as the hypnotism spell (2-5 rounds), or some other drug, all with a normal save vs. poison. There are only three doses; then the fangs merely pierce. A present creator can refill it in two rounds, and one cobra reputedly regenerated its venom in 24 hours. A dose suits one human-sized victim, so adjust for size.

Cobras served as treasure guards, bodyguards or assassins. Given a target's true name, one tracks that person within one mile by the psychic vibrations tied to the name; mind blank or similar magic blocks them. It knows only a few simple commands set at its making, such as guard, attack, hide, track and come home, plus activation words. Programming stays fixed until it is deactivated (dispel magic, for instance) and reset by its creator. Electrical attacks like lightning bolt or shocking grasp have a 10% chance to scramble it into uselessness.

It never eats, sleeps or breathes. The craft was lost centuries ago, and only a few dozen were ever built. A working, deactivated cobra sells to wizards for 2,000 gp if its command words are known.