This is a fairly accurate description, and bears a suspicious resemblance to Marrangha magic first developed in Dree and the ghastly experiments of Xakhaz. Notura can used in many ways, from cursing someone's luck and erecting a painful defensive barrier, to wiping part of their memory or conjuring a phantasm of sorts to destroy them utterly. Karam Gruul discovered that, if brought fully into the Earthly Plane, an Ectoplasmic Lurker would release Notura upon its death - hence, he always kept one imprisoned nearby in the event of emergences.
However, as with everything of a magical nature, Notura could be countered by certain items possessed of the same or similar mystical qualities - these became known as the Wards of Notura - and many were lost over the years since Gruul's initial defeat. Van Heldenghast thankfully located a number of these and led a Bounty Hunter, who had once been a victim of Gruul's Notura, to retrieve as many as possible and thereby survive arresting Gruul and bringing him to justice.
Since Gruul's imprisonment, it is unknown whether or not Notura is still practised by his apprentices, if he had any he trusted enough to teach this dark art.