The Skavis was a pale, effeminate-looking male, who hid himself under the guise of Priscilla of the Ordo Lebes. As such, he always wore turtlenecks to pass a one of the Ordo's women. He was intent in abducting and killing off practitioners in an effort to cull off potential progenitors for wizards and framing the Wardens.
In White Night, the Skavis puts Elaine Mallory under a psychic attack of despair making her attempt suicide. Harry mind-talks to her, warns her what's happening. Elaine fights off the Skavis attack then blasted him from the building with: Fulminaris.