One Part Agony, Three Parts Cold Wought Iron is a Tome of Knowledge Bestiary entry for Flayerkin.

Instructions: Order & Destruction

This unlock is completed in 4 parts:

1.7k 41.5k - in High Pass

Loot "Flayer-Kin's Scaling Chains" from a corpse "Dead Flayerkin", inside the Tomb of the Traitor (5.2k 39.3k).

9.7k 49.1k - in High Pass

Loot "Flayerkin Hooks" from another corpse "Dead Flayerkin" inside a cave.

47.6k 33.2k - in West Praag

Loot a "Flayer-Kin's Iron Helm" from another corpse "Dead Flayerkin" inside the calls. He is near a bush, a well and an empire home.

Then turn the items in:

For Order: To "Breitenhoff the Faithful" by a campfire at Empire Chapter 17 in Praag at 12.7k 57.4k.
For Destruction: To "Kreelik of Clan Moulder" a skaven by the central campfire in Chaos Chapter 17 in Praag at 6.5k 9.7k.

Rewards