This WoW set features the full Conqueror’s Kirin Tor transmog, which is the mage tier 8.5 (25-man) raid set. Kirin Tor 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 Mage Tier 8.5? By purchasing from vendors and slaying Ulduar bosses.
How Many Set Pieces?  Helmet, Shoulders, Chest, Hands, and Pants
Mage Tier 8.5 Transmog: [25-Man Drop Locations]
Head: Crown of the Wayward Vanquisher [Purchase from vendor] in Dalaran.
Chest: Breastplate of the Wayward Vanquisher [Purchase from vendor] in Dalaran.
Hands: INSERT [Gauntlets of the Wayward Vanquisher] in Ulduar.
Legs: INSERT [Legplates of the Wayward Vanquisher] 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 Kirin Tor Garb (hover for set bonuses)
Shoulder: Conqueror’s Kirin Tor Shoulderpads
Chest: Conqueror’s Kirin Tor Tunic
Hands: Conqueror’s Kirin Tor Gauntlets
Legs: Conqueror’s Kirin Tor Leggings
Optional: Hands and Legs low droprate from [Emalon the Storm Watcher] in Vault of Archavon.