Reach the antenna room and destroy it | Walkthrough The Last Guardian Guide

Eliminate enemies by lighting them with your mirror

Climb onto the healed-up Trico, and begin the climb to the tower where the encounter with the beast took place. The heroes are soon attacked by the first armor standing one of the balconies. Use the mirror to target the enemy and wait until a lightning hits him. Use the same method to eliminate the second suit of armor on one of the higher balconies.

Once you've reached the highest level of the tower, aim the mirror at the wooden barricade shown on the screenshot. The lightning will destroy it, and Trico will be able to reach the newly unlocked part of the tower.

The new corridor leads to a room with another cage. Once you enter the cage, the antenna starts affecting Trico, but unlike previous scenes, the monster will try to withstand its influence, and won't attack the boy. Destroying it will make Trico regain full control over his mind.