This WoW set features the full Nordrassil transmog, which is the druid tier 5 raid set. Nordrassil 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 Druid 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
Druid Tier 5 Transmog: [Drop Locations]
Note: Druids have three different sets with the same exact look. Tier 5 druid armor tokens can be used to purchase any of the set pieces.
Head: Helm of the Vanquished Defender by slaying Lady Vashj in Serpentshrine Cavern.
Chest: Chestguard of the Vanquished Defender by slaying Kael’thas Sunstrider in The Eye.
Hands: Gloves of the Vanquished Defender by slaying Leotheras the Blind in Serpentshrine.
Legs: Leggings of the Vanquished Defender by slaying Fathom-Lord Karathress in Serpentshrine.
Tier 5 Set Vendors: [24,27] Kelara (Aldor) OR [44,91] Veynna Dawnstar (Scryer) | ~Shattrath City~
Set Name: Nordrassil Harness (hover for set bonuses)
Shoulder: Nordrassil Feral-Mantle
Chest: Nordrassil Chestplate
Hands: Nordrassil Handgrips
Legs: Nordrassil Feral-Kilt
Set Name: Nordrassil Raiment (hover for set bonuses)
Shoulder: Nordrassil Life-Mantle
Chest: Nordrassil Chestguard
Hands: Nordrassil Gloves
Legs: Nordrassil Life-Kilt