This WoW set features the full Conqueror’s Deathbringer transmog, which is the warlock tier 8.5 (25-man) raid set. Deathbringer is obtained by looting tokens from Wrath of the Lich King bosses and purchasing some set pieces via Dalaran tier vendors with gold.
How to Get Warlock Tier 8.5? By purchasing from vendors and slaying Ulduar bosses.
How Many Set Pieces?  Helmet, Shoulders, Chest, Hands, and Pants
Warlock Tier 8.5 Transmog: [25-Man Drop Locations]
Head: Crown of the Wayward Conqueror [Purchase from vendor] in Dalaran.
Chest: Breastplate of the Wayward Conqueror [Purchase from vendor] in Dalaran.
Hands: Gauntlets of the Wayward Conqueror [Mimiron] in Ulduar.
Legs: Legplates of the Wayward Conqueror [Freya] in Ulduar.
Head/Chest Vendor (Alliance): Arcanist Ivrenne [37,55] in Dalaran.
Head/Chest Vendor (Horde): Magistrix Lambriesse [65,23] in Dalaran.
Redeem Token Vendor: Paldesse [43,49] in Dalaran.
Set Name: Conqueror’s Deathbringer Garb (hover for set bonuses)
Shoulder: Conqueror’s Deathbringer Shoulderpads
Chest: Conqueror’s Deathbringer Robe
Hands: Conqueror’s Deathbringer Gloves
Legs: Conqueror’s Deathbringer Leggings
Optional: Hands and Legs low droprate from [Emalon the Storm Watcher] in Vault of Archavon.