At the end of Hunger in the Dark, after you complete the finale and cross the bridge, a bunch of trolls show up to get exploded by the bomb you placed. If you tag one of these trolls before they die, the UI will display a boss healthbar with a placeholder image and a name of <CHAOS_DUMMY_TROLL>.
I would venture it’s a bug. usually anything between < > tags are. It would be fun if we could have a whole troll fiesta! I remember thinking when I first played V2 I was on a timer and if I didn’t ring the bell, I’d have a troll swarm on me.