This WoW set features the full Valorous Deathbringer transmog, which is the warlock tier 8 (10-man) raid set. Deathbringer is obtained by looting tokens from Ulduar and trading those tokens in for set pieces via Dalaran tier vendors.
How to Get Lock Tier 8? By slaying Wrath of the Lich King Ulduar bosses.
How Many Set Pieces?  Helmet, Shoulders, Chest, Hands, and Pants
Warlock Tier 8 Transmog: [10-Man Drop Locations]
Head: Helm of the Wayward Conqueror [Mimiron ] in Ulduar.
Chest: Chestguard of the Wayward Conqueror [Yogg-Saron] in Ulduar.
Hands: Gloves of the Wayward Conqueror [Freya] in Ulduar.
Legs: Leggings of the Wayward Conqueror [Hodir] in Ulduar.
Redeem Token Vendor: Paldesse [43,49] in Dalaran.