This is a much harder boss than Sapphiron. This one has three assistants:
Vesperon: 25% less Health as long as he lives
Shadron: 100% more firedamage until he's dead
Tenebron: Annoying adds with a sunderarmour (as long as he's on the ground) and 100% more shadowdamage until he's dead

Sum: Bossmelee + 3 bigaddmelee + smalladdmelee + fire/shadow-breaths + sunderarmour + avoid the voidzones (i think they are still instandkills)

Songs:
Fort Minor - Remember The Name
Two Steps from Hell - Breath Of Ran Gor
Two Steps from Hell - United We Stand, Devided We Fall
Dope - Die Motherfucker Die