History of High Revenants

High Revenants are the marked enemies that must be defeated before a Revenant Baron's shield can be broken. In the Captive Memories mission, three High Revenants appear in each of the two combat arenas, and defeating the marked enemies drops the Baron's shield. Once the shield is down, the Baron is killed and the totem its soul leaves behind must be destroyed quickly, or the Baron is revived at full health.

Skolas

The same mechanic returns in the fight against Skolas. At 50 percent health he becomes immune to damage and three High Revenants appear; defeating all three breaks his shield so the fight can continue.

Guides from different patches vary, so details may have changed since the mission was released.