Keep your distance from the boss so that you can see their attacks coming. Shoot the skulls it summons to avoid taking damage from them, and stay away from the mini-volcanoes it summons. The Electric Burst attack will be very noticeable once it has started, since the boss will teleport to the middle of the arena with an electrical ball underneath it. This is when you are supposed to use your charged Ragnarok DG-4s to stun the boss to proceed to the damage phase, preventing the attack. However, if you cannot prevent the attack, you must hide behind one of the four pillars in the arena to be safe from the attack, otherwise, you will be instantly downed.

The best weapons to damage the boss are the following (all Pack-a-Punched): Ray Gun, XM-53, and Mustang & Sally. The upgraded bow's uncharged shots can be spammed as a last resort if you cannot pull one of these weapons from the box. You can also read the full, detailed boss fight guide for the main quest, My Brother's Keeper.