Maighread's Necklace

After the gold sidhen deities banished their traitorous daughter, Maighread, and her followers to the aphotic plane of shadow parallel to Namkural, it was widely assumed that they would perish under those inhospitable conditions. Indeed, nearly all records of this event have been lost -- lending to the apparent mystery of where and when the siabhra originated. In reality, it was Maighread's own magic that allowed those loyal to her to survive and adapt to their new home, eventually evolving past the realm of what was known to sidhe and into the monstrous siabhra. By the time she succeeded in breaking the wards that completely banished them from Namkural, none in living memory still recalled that they had even existed.
But their adaptation to the aphotic plane was hardly without its trials. Early in their banishment, a group of sidhe most loyal to the self-styled Queen set out to explore the boundaries of the mirrored plane. Knowing that the dark magic there could warp and twist reality, Maighread enchanted one of her prized possessions with a warding beacon meant to protect the explorers and allow them to return to their newly-established fortress safely. This choker-style necklace, dripping with rubies and garnets, was the best insurance that she could offer those performing this undertaking.
What ultimately befell the exploration party remains unknown, even to the siabhra. Whatever magical disaster that did occur corrupted them, twisting them into the first cannibalistic, psychotic redcaps that now plague Namkural like a hungry tide. Maighread's necklace was lost, but presumably still exists somewhere on the aphotic plane. With its location unknown, no patrols of Dullahan that have gone searching for it have ever turned up a trace of it. Nevertheless, the siabhra consider it one of their most important lost artifacts.