The strategy for defeating Caltheris in the first phase is simple, kill zombies to charge the lightning towers while avoiding the slow-moving laser that tracks you. When the toxic gas cloud appears, move to the top floor of the arena and do your best to avoid the lasers while taking out zombies.

Phase 2 is when the real fight begins. Constant movement is key, and you'll need to dodge the rock throw to avoid taking massive damage to your armor. Use the wall-jump mechanic to fly through the air with anti-gravity to avoid the boss from catching up to you, but be careful, as you are vulnerable to the rock throw while in mid-air. Use the LGM-1 wonder weapon to take out the boss's armor and reveal a Blue Crit Spot, and then switch to your main damage weapon to focus fire on the crit spot.

Phase 3 is very similar, with a bigger, faster, and stronger Caltheris, but with the same attacks and strategy. The ground slam in this phase is devastating so ensure you are off the ground or far enough away to avoid being hit by this attack.

Phase 4 is the final phase, and the most dangerous one by far, you need to strategically position yourself to have the boss throw the rocks in locations that do not hinder your ability to move around the arena, as each rock will leave a lethal pool of aetheric energy on impact. As long as you can control where the pools are, you can survive this fight and deal damage while wall-jumping and/or jumping off the top level and shooting the boss.