The shadar-kai are an enigmatic people who inhabit the Shadowfell, a bizarre new plane that appeared after the Puncture. They are death worshipers who swear allegiance to a power they call the Raven Queen. Only the shadar-kai know whether the Raven Queen is a goddess of death, a poetic name for the concept of death itself, or something even more sinister.
The evaporation into nothingness of all the life of Multiverse B‘s Material Planes during the Puncture meant that the Raven Queen was denied her due. The shadar-kai took none too kindly to this and, blaming human magical experiments for the event, began attacking human settlements on the Material Planes. It was through Seth Mase’s intervention that the shadar-kai were convinced to desist, even leaving the door open to allying with the humans of Multiverse A against their common foes.