When Roy's black ice blocked his vision, Mundus, who was inside the shield of the Wall of Sighs, realized that something was amiss.
To him, be it Sparda or Osiris, they were both enemies that he had to be vigilant of. Now that they had suddenly joined forces to block his vision, they definitely planned to do something against him. He absolutely could not let them succeed.
Thus, he frantically attacked from inside the shield, attempting to break Roy's frost blockade.
Roy went all out this time and continuously output his magic power without holding back. He did not choose to fight against Mundus's magic power but instead used an instant repair method. Wherever the frost shield broke, he would immediately replenish it and maintain the effect of blocking Mundus's vision.
Even so, Roy's magic power was rapidly depleting. Fortunately, with the high-speed magic power recovery of the Cold Winter Armor, he did not exhaust his magic power.