Twilight Cultist

    While in Silithus and retrieving Encrypted Twilight Texts for Hermit Ortell (after a chain of quests, he starts True Believers which rewards Decoded True Believers Clippings containing blacksmithing and tailoring patterns) or Bor Wildmane (returning the texts to him gives reputation with the Cenarion Circle) I was able to collect several Twilight Trappings sets (only one of the items was rarer than the two others, I'm not sure which one it was). It's supposed to give an evil aura from the description, but even though it is not visible it does have this feel. Unfortunately, since these cloth items don't get soulbound, they cannot be used for transmogrification.

Head: Twilight Cultist Cowl
Shoulder: Twilight Cultist Mantle
Back: Mantle of Desire
Chest: Twilight Cultist Robe
Shirt: Ebon Filigreed Doublet
Hands: Bat Fur Mitts
Waist: Deathmage Sash
Weapon: Crystalfire Staff

The appropriate mount in name: the beautiful Twilight Drake.

In addition to this outfit, there is a quest, Dressed to Kill, in Twilight Highlands, that permits us to disguise into a twilight's hammer cultist.