The goal in this 3 part activity is to take out certain enemies shimmering with a blue color. They will drop a battery that the Guardian must throw into the forge to charge it and progress. There are three waves, followed by a boss.
One more goal in the forge is to take down two drones (similar to the saboteur drones) that spawn with the second wave. One is located at the stone pillar at the water on the left side (if you come from the entrance) and the second spawns in the cave (on the right side from the entrance). They despawn after some time and are gone before the third wave starts. Taking down these drones provides the "Maximum Temper" perk that provide more and better loot. In the mystery box quest, the player needs to take out these drones at every forge.