The "Hunt for the Harbinger" is a story questline (Patch 10.2.7) that sets the stage for the War Within expansion.
: They change tactics and gain new abilities as their health drops. Destiny 2: The Harbinger Mission & Title The HarbingerHD
: Focuses on Alleria Windrunner tracking a mysterious Void entity known as Xal'atath (The Harbinger). The "Hunt for the Harbinger" is a story questline (Patch 10
: Complete a master-level Hunt without any team deaths. The HarbingerHD
: Found in the EDZ, accessible through a fireplace in the building near the Lake of Shadows strike.