Requirement
Reach Exalted with one of the four battleground reputations.
Detail
Factions: The Defilers or League of Arathor.
Factions
The Defilers or League of Arathor
Notes
Blizzard's article counts four battleground reputations without naming them; the battleground and its two factions are from Wowhead's reading of the client.
Confidence note
Challenge and points: Blizzard's article. The client's challenge name, factions: Reported (one outlet).