The main hazards are Damage Walls and Bounce Obstructors. Therefore you need all Pierce Null Damage Wall monsters. You can deal with only 3 NDW monsters but you have to turn adjust so that the non-NDW monster will start on the first turn. Before the Boss Stages, the Drone has a 9 Turn Volatile Blast that can nearly one-shot you. Since the Drone cannot be broken, even with Drone Breakers, you need to clear all the mobs within 9 Turns Only on the 3rd Stage, the Obstructors' HP is higher. In order to one-shot them, you need a Fire monster whose ATK can reach 31,935 after Gauge.