The Swill

The Swill is one of the most powerful known Hexblades. It resides in the Shadowfell and its point of contact on the material plane is the sword Absciser, which was hidden in an icy cave on the shores of Alishikta when Zachár Flame-tongue struck a pact with it, though it has since vanished. The Swill is most known on the material plane for its pollution of Paper Fern Lake through Zachár in October of EL 1000.
In 1008, the first known adventuring party to travel to the Shadowfell since the Light Brigade reported that, according to the shadar-kai they had encountered there, the Swill had declared all-out war on the Raven Queen.