Crown of the Lost Vanquisher

Crown of the Lost Vanquisher is a tier 7 armor token. It can be exchanged in Dalaran for the following items:
 * Valorous Bonescythe Helmet
 * Valorous Scourgeborne Faceguard
 * Valorous Scourgeborne Helmet
 * Valorous Frostfire Circlet
 * Valorous Dreamwalker Cover
 * Valorous Dreamwalker Headguard
 * Valorous Dreamwalker Headpiece

Source
This item drops from Kel'Thuzad in the 25-man version of Naxxramas.