A Destroyer Chest spawns after defeating Plague of Destruction and its accompanying group.
Plague of Destruction can be easily defeated by having Engineer Xapp activate the surrounding trap towers and luring it inside.
This boss deals upwards of 200-300 damage with his skills. Bringing a Ritualist with Shelter can help a lot. Also, due to the AoE nature of his attacks, Pain Inverter can help to quickly take him down.