You are unlikely to encounter any of these warriors directly, but should you find yourself face to face with a skull-faced giant in power armour in the middle of the night, welcome him with open arms – he is most likely a Reiver.*
If any of the following details are also present – red wings on the helmet, flayed hides, or a corona of daemonic lightning – immediately consult Volume 2 of the Infantryman’s Threat Identification Field Guide, 49th edition, section ref. 17.a66.4111 – Hereticus Majoris (revised)
https://regimental-standard.com/2017/06/28/...ear-the-reiver/