The magical ring that produces new copies every ninth night is Draupnir.
Draupnir is a gold ring belonging to Odin in Norse mythology. Its supernatural power is that every ninth night, eight new rings emerge from it, each matching the original in size and weight. Thus, the ring effectively produces nine rings in total when the original is counted, which is why summaries sometimes describe it as multiplying ninefold.
The dwarf brothers Brokkr and Eitri, also called Sindri in some traditions, forge Draupnir. It is one of three remarkable gifts produced during a contest involving Loki and the Sons of Ivaldi. The other notable creations are Thor’s hammer Mjölnir and Freyr’s boar Gullinbursti. Draupnir’s name is usually connected with the idea of dripping or emanating.
Odin places the ring on the funeral pyre of his son Baldr. Hermóðr later retrieves it from the realm of the dead. Draupnir should not be confused with Andvaranaut, another famous enchanted ring associated with the dwarf Andvari and the cursed treasure later linked to the Völsung cycle.