I don’t know what this is, beyond a “Spindle Drone” from the upcoming Warhammer Quest: Blackstone Fortress game, but it sure has got me interested and excited to find out more! In 25 years, I can’t recall ever before seeing or reading about anything like it in the Warhammer 40,000 lore.
Given the setting of the game, and some of the teases, it seems likely it’s tied to either the Eldar/Old Ones or the Necrontyr/C’Tan. But the legs and the curves of the armour remind me more of the Tyranids than anything else, despite it appearing to be (entirely?) mechanical.
Blackstone Fortress should be out by the end of November, so it shouldn’t be too long before we get some answers.