If one is to pick the ultimate Polaris villain, that has to be the psychic entity known only as Malice. A member of Mr. Sinister's Marauders, and their field leader, Malice is an incorporeal creature that possesses her victims to do her bidding. After possessing Alison Blaire a.k.a. Dazzler for a time and create discord among the X-Men, Malice found a new home in Polaris' body soon after. During this time, Polaris became an enemy of the X-Men, and Malice sure made their life miserable, particularly during the events of "Inferno". The only distinctive sign that Malice has taken possession of someone is the choker that her victims wear in their necks.
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First appearance Uncanny X-Men 214 (1987)
Created by Chris Claremont and Rick Leonardi