This enemy from a CM in Zeffo seems to be invincible. I let it run for over 30 minutes and it would not die. Seems like its health would not go below 90%, and it would keep healing to 10% protection. This occurred in the current phase (phase 5), and worked fine in phases 3 and 4. The attached video is a short clip that shows this, after having already run it for 30 minutes right before I forfeited the attempt.
