Undying Untargetable Rare (Archer Transcendent?)

Hello! On a Vaal Factory map layout, got a rare monster that is untargetable, doesn't die, attacks and damages me, and prevents map completion. I can't identify it at a glance, but it seems similar to an Archer Transcendent. It looks like an engineer guy that crawls around on his belly and shoots little bullets from his robotic legs? I snapped a picture for you while trying not to die to it, hope that helps.



https://imgur.com/a/rsYm1mZ

Bug Report ID: #713379601