This WoW set features the full Tirisfal Regalia transmog, which is the mage tier 5 raid set. Tirisfal Regalia is obtained by looting armor tokens from various Burning Crusade bosses. These tokens can be traded for set pieces via Shattrath City tier vendors.
How to Get Mage Tier 5? By slaying Serpentshrine Cavern and The Eye (Tempest Keep) bosses.
Are There Multiple Tier 5 Transmogs For My Class? No, some classes do have multiple tier 5 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 5 set)
How Many Set Pieces?  Helmet, Shoulders, Chest, Hands, and Pants
Mage Tier 5 Transmog: [Drop Locations]
Head: Helm of the Vanquished Hero by slaying Lady Vashj in Serpentshrine Cavern.
Chest: Chestguard of the Vanquished Hero by slaying Kael’thas Sunstrider in The Eye.
Hands: Gloves of the Vanquished Hero by slaying Leotheras the Blind in Serpentshrine.
Legs: Leggings of the Vanquished Hero by slaying Fathom-Lord Karathress in Serpentshrine.
Tier 5 Set Vendors: [24,27] Kelara (Aldor) OR [44,91] Veynna Dawnstar (Scryer) | ~Shattrath City~