Harbinger of the Second Trial
From WoWWiki
The Harbinger of the Second Trial is located in Eversong Woods. [43.3, 28.7]
This gem will appear once 
[20] The Second Trial is accepted.
Objective of
Using this object will summon 
Champion Bloodwrath, then Champion Lightrend, then Champion Swiftblade, and finally Champion Sunstriker. All of them must be defeated to complete the quest [20] The Second Trial.
