The necrophidius is a relatively standard tomb guardian, burglar alarm, and low-level assassin. It can also be easily upgraded with contact poison, enchantments, magic fangs, and other nasty effects. Your average necrophidius will be found in a dungeon, so here are a few less likely examples...
A necrophidius lurks in the gibbet cage at the crossroads, masquerading as a corpse. Left as a trap for a meddlesome spellcaster, it attempts to daze and paralyze anyone in the robes of a wizard, cleric, or friar. The battlemage who commanded the necrophidius intended to come back and humiliate his frozen rival, but was killed in border skirmish the next day. The necrophidius has remained here ever since. It has not been discovered because the road is little used, and scavengers make quick work of the construct’s victims—coyotes during the day, chupacabras at night.
A desperate rogue stabbed a necrophidius in the eye sockets with an intelligent +2 serpentbane dagger, wedging it in its skull. The resulting magical feedback warped the dagger’s intelligence even as it transferred it into the construct. Now the necrophidius is convinced he is Noble Hood, an undead guardian naga and heir to a reptile kingdom. He demands to be treated as such should anyone find the treasure chamber he guards. Noble Hood instinctively fears removal of the enchanted dagger from his skull and will attempt to slay anyone who approaches too close. If the dagger is removed, the construct (assuming it has not already been destroyed) returns to mindlessness, but the dagger never quite recovers, sympathizing with the snakes, serpentfolk, and nagas it is meant to slay.
What was a river delta trading post at the foot of a school for female necromancers has grown into a small city—but the mages are no less in charge. The gynarchy of Osdela Dame has grown into a thriving university town where the living share the streets with the bleached bones of the shambling dead. Necrophidiuses are popular pets of the necromancer elites, who walk them in the streets as if they were dogs. Typically a necromancer uses a former paramour’s head in the construction—it is a way of keeping one’s old lover close and reminding one’s current lover of the price of disloyalty.
—Pathfinder Bestiary 2 196
Apparently the necrophidius was born in White Dwarf. In the last two to three years I’ve started avidly reading White Dwarf even though I’ll never play the games. If that’s not the nerd equivalent of pornography, I don’t know what is.
The necrophidius’s method of construction raises the question: Who looks at a python skeleton and thinks, “That would look even better with a human head”? What kind of person treats taxidermy like a mash-up? I mean, besides my coworker R.…