The Mark of the Illidari can be exchanged for flasks whose usage is restricted to raid instances.
Source
This item drops from trash mobs in World of Warcraft: The Burning Crusade raid instances: Serpentshrine Cavern, Tempest Keep, Black Temple, Battle of Mount Hyjal and Sunwell Plateau.
Notes
To exchange this item for a flask, players must have exalted reputation with the Aldor or Scryers, the Sha'tar, and the Cenarion Expedition.
Gives:
Patch changes
- Patch 7.1.5 (2017-01-10): Now has a vendor price.
- Patch 2.1.0 (2007-05-22): Added.