Also known as the Horn of the Hunter, or the Horn of Madness, it was once Doyle's long ago, before the weirding stripped him of much of his power.
Only the huntsman of the wild hunt may touch it without going mad, and then only when the magic of the hunt was upon him. Doyle explained that he was the huntsman, he was always the huntsman.
It was returned to him by the skelatal brides of the sluagh sithen in Swallowing Darkness.