With the release of Fall of Oriath, Path of Exile will also have another new challenge league. This time, its called Harbinger and involves a new and unknown invading force called the Harbingers.
The Harbingers will randomly appear and continuously summon their monsters after you, the only way to damage the Harbinger is to defeat their invading force. Defeating a Harbinger can yield new currency items and new unique item parts.
As always there will be a total of 40 new challenges that can be completed throughout the whole league. Completing each interval of 12 will reward a specific reward. After the 19th challenge, every consecutive 3rd challenge after that will reward a hideout totem piece.
Harbinger league will launch simultaneously with the Fall of Oriath expansion on August 4th.