The Undying Essence is the 9th boss of Enigmata: Genu's Revenge. It is a boss with 3 drones, all of them has a drain shield surrounding them, and the boss itself also has a drain shield in the center. These shields will increase the boss' health if you shoot them instead of reducing it. Unlike the Reversion though, these drain shields will INSTANTLY be recreated after being disabled by the Destroy Shield skill, so don't bother taking out the drones. Instead, try to engage it from the sides and shoot its wings when the drones are not blocking the way. The drones and the boss can all also shoots lasers that can cause your weapons to stop for a short period of time. All of its other attacks are pretty generic and weak though, so it can even be easier than Pyre Guard if you know the tricks.