The Frenzied Black Drake is a level 54 black drake spawned when a player talks to Cyrus Therepentous during the quest 
[54] A Taste of Flame. This quest requires a player to obtain a Black Dragonflight Molt which can either be obtained through [Hoard of the Black Dragonflight] received at the end of the [48] Divine Retribution questline or by slaying and looting the Frenzied Black Drake.
Notes[]
Prior to patch 2.3, this drake used to be elite and very difficult to solo, forcing many players obtaining the Molt through Divine Retribution, alas this is no longer the case, and Frenzed Black Drake can easily be solo'd now. It is also worth noting many players didn't know any better that talking to Cyrus Therepentous would spawn an elite dragon, and very often Therepentous' cave would be fulled of player corpses or skeletons.