This WoW set features the full Valorous Cryptstalker transmog, which is the hunter tier 7.5 (25-man) raid set. Cryptstalker is obtained by looting Wrath of the Lich King bosses and purchasing some set pieces straight from the vendor with gold. Dropped tokens can be traded for set pieces via Dalaran tier vendors.
How to Get Hunter Tier 7.5? By purchasing from vendors and slaying Naxxramas/Obsidian Sanctum bosses.
How Many Set Pieces?  Helmet, Shoulders, Chest, Hands, and Pants
Hunter Tier 7.5 Transmog: [25-Man Drop Locations]
Head: Crown of the Lost Protector [Kel’Thuzad] in Naxxramas
Chest: Breastplate of the Lost Protector [Gluth] in Naxxramas
Hands: Gauntlets of the Lost Protector [Sartharion] in The Obsidian Sanctum
Legs: Legplates of the Lost Protector [Purchase from Vendor] in Dalaran.
Shoulder/Leg Vendor (Alliance): Arcanist Ivrenne [37,55] in Dalaran.
Shoulder/Leg Vendor (Horde): Magistrix Lambriesse [65,23] in Dalaran.
Redeem Token Vendor (Both): Bragund Brightlink [51,72] in Dalaran.