History of Blighted Skirmish

'''Blighted Skirmish''' is a Pale Heart Pathfinder triumph from Destiny 2: The Final Shape: travel to The Transgression and claim the reward for defeating Ithriks, the Lost.

How to complete

1. Go to The Transgression in the Pale Heart.
2. Find and kill Ithriks, the Lost, a Taken Captain Major. Destinypedia lists Arc Shrapnel Launcher, teleportation, an Arc Darkness Bolt, rapid movement and summoning of Taken as his abilities, plus high durability, so expect adds and bring Arc-resistant caution.
3. Open the reward chest he leaves behind (the objective is "Chests").

The exact spawn trigger for Ithriks is unconfirmed in the sources I opened.

Rewards

A search summary of light.gg lists a Ghost Reputation Increment; I could not open that page.