This WoW set features the full Voidheart Transmog, which is the warlock tier 4 raid set. Voidheart is obtained by looting armor tokens from various Burning Crusade bosses. These Tokens can be traded for set pieces via Arodis Sunblade (Scryers) or Asuur (Aldor) located within Shattrath City.
How to Get Warlock Tier 4? By slaying Karazhan, Gruul’s Lair, and Magtheridon’s Lair bosses.
Are There Multiple Tier 4 Transmogs For My Class? No, some classes do have multiple tier 4 sets (depending on their class trees), but every tier set variation features the same exact transmog look. For example, the paladin has a different set for retribution, holy, and protection, but all three sets share the same exact model and color variation. (Hunter, Mage, Rogue, and Warlock feature only one tier 4 set)
How Many Set Pieces?  Helmet, Shoulders, Chest, Hands, and Pants
Warlock Tier 4 Transmog:
Head: Helm of the Fallen Hero by slaying Prince Malchezaar in Karazhan.
Chest: Chestguard of the Fallen Hero by slaying Magtheridon in Magtheridon’s Lair.
Hands: Gloves of the Fallen Hero by slaying The Curator in Karazhan.
Legs: Leggings of the Fallen Hero by slaying Gruul the Dragonkiller in Gruul’s Lair.