From Lexicanum

The Vexanthrope is a fragile mask of flayed skin and bones which is inscribed with runes of hallucination and confusion. This gruesome mask is usually worn by the Dark Eldar Archon of a high ranking Kabal, as it is arcane, and incredibly rare. Eventually, it will fuse to it's wearers face. A Vexanthrope is able to psychically cast an illusion into the minds of the onlookers closest friend or most treasured love.¹

Sources

• ¹:Codex Dark Eldar 3E, p.15