Shadow of Angst: Who the hell just spawned in my mission??

This guy spawned about a minute after I killed the acolyte. I know Angst is a regular acolyte enemy, but wtf is a "Shadow of Angst"? In any case, he didn't drop an arcane or Steel Essence on death, so I have no idea what this was and can't find it on the wiki. Anybody know what this is or where I can read up on this? https://preview.redd.it/6xdyboc5lu491.jpg?width=1280&format=pjpg&auto=webp&s=31778491d027f3b6ed265af29965e06ff64b1303 submitted by /u/NerfCommando64 [link] [comments]

source https://www.reddit.com/r/Warframe/comments/v9fz8o/shadow_of_angst_who_the_hell_just_spawned_in_my/