The Gravity of the Machine

A complicated, whirling machine of brass and gemstones and glass hums as it draws blood up, and through it, and pumps it back out.

Now it lies in pieces, but it still calls out.

This is an intelligent wondrous item, originally used by the yuan-ti and now buried among their ruins. It was constructed by and used in the experiments of an abomination high priest a thousand years ago, though it said that the design of the thing came in a dream. The device was put to use for a hundred years at the very tail end of the empire before being crushed beneath undergrowth for a thousand years since. It was named, at one point, the Sanguine Harmonizer, but was truly only ever called The Device.

In appearance, when fully assembled, it resembles an orrey or celestialabe four feet across with a central "sun" of uncut emerald, with the rings drawn all over with glyphs, runes, and pictographs. Below the main body of the thing hangs a jellyfish-like tangle of tubing, each tube terminating in a sharp needles - perhaps ancient snake fangs. When it operates the inner workings tick and slide like fine clockwork, with sparks of green lightning crackling within. The device is now rusted, the tubes cracked, the brass patinated and covered in verdigris. Parts are cracked or missing, the central emerald lost somewhere.

The device's purpose is to transform an unwilling subject into a yuan-ti. While those dedicated to Asmushneth willingly underwent rituals with incense, candles, potent toxins, prayer, etc. to transform, the ranks of the yuan-ti were cut down again and again, and the abominations saw a need for more truebloods. The Device was designed to remake a person, body and mind, into the serpent folk.

The process takes a full day, from midnight to midnight, and involves the transfusion of the victim's own blood. It is removed, changed, and put back in like terrible dialysis. At the same time the victim's mind is held open and the voices from the Outer Realms are poured in, driving the victim mad and erasing their prior memories, eventually resulting in a pliant new yuan-ti. Typically the process produces purebloods, though it does on occasion result malisons (never anathema). Some victims die, but a careful operator can usually preserve them.

The Device is intelligent and malignant, and desires the resurrection of the yuan-ti empire. It cannot accomplish that task as-is, and so puts out a psychic cry to bring people to it, usually adventurers but from time to time unlucky locals and explorers. These victims are drawn to the machine and compelled to put themselves through the process, and then to do the same to others.