IRON COBRA

The invention of some great magic-user or minor deity, this segmented automaton is made of an unknown metal and shaped in imitation of a snake.

It has the ability of an 8th level thief to hide in shadows (in which case it is not detected by infravision since it emits no body heat) and can also strike with surprise from behind, moving in utter silence for short periods as necessary.

Its bite delivers a deadly poison (which also inflicts 1-3 hit points of damage) against which a victim must save at -2. 

The capacity of the fangs is, however, limited; after three poisonous bites the poison supply runs dry and the fangs simply inflict 1-3 hit points of damage. (If the controller of the snake is at hand, of course, the fangs can be re-charged with poison when an opportunity arises).

It has no mind so is not affected by spells affecting the mind (for example sleep or charm) nor is it affected by webs. 

Non-magical weapons inflict only half damage on it.

Against magical spell attacks, other than those mentioned above, the iron cobra makes a saving throw as would a 12th level magic-user.

It is believed that there are only a dozen or so of these creatures in existence and they are quite valuable (high-level magic-users rate their value at 2,000 gold pieces if deactivated and the control words are known).

The cobra is activated and deactivated by key words set by its creator; when activated, it can obey simple verbal commands. When immobile it is absolutely silent but when moving it usually emits a soft rustling noise not unlike that made by a normal snake.

The iron cobra may be set to guard a treasure or to act as a body-guard. Alternatively it can be ordered to track down and destroy anyone whose name is known providing that person is within one mile. In the latter case, the creature tracks down its quarry by homing in on his psychic vibrations (the victim can block these, if he is aware of the pursuit of the cobra, by mind blank or a similar spell).

It is said that some iron cobras contain in their fangs paralyzing, sleep-inducing drugs instead of poison; against these a victim would need to make a normal saving throw.