This WoW set features the full Heroes’ Bonescythe transmog, which is the mage tier 7 (10-man) raid set. Bonescythe 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 Mage Tier 7? By purchasing from Dalaran vendors and slaying Naxxramas bosses.
How Many Set Pieces?  Helmet, Shoulders, Chest, Hands, and Pants
Mage Tier 7 Transmog: [10-Man Drop Locations]
Head: Helm of the Lost Vanquisher [Kel’Thuzad] in Naxxramas
Chest: Chestguard of the Lost Vanquisher [Purchase from Vendor] in Dalaran.
Hands: Gloves of the Lost Vanquisher [Purchase from Vendor] in Dalaran.
Legs: Leggings of the Lost Vanquisher [Thaddius – Gluth] in Naxxramas.
Chest/Hand Vendor (Alliance): Arcanist Ivrenne [37,55] in Dalaran.
Chest/Hand Vendor (Horde): Magistrix Lambriesse [65,23] in Dalaran.
Redeem Token Vendor (Both): Paldesse [43,49] in Dalaran.