After you make your way through Hyrule Castle in the Still World, you fight an echo of Ganon.

How to Defeat Ganon

First Phase

Ganon will spin his trident, then disappear and reappear in a different location. He will draw back the trident, then stab toward you with it, so keep moving so that you aren't in the path that he is aiming at.

You can bind to the trident and pull on it to make him drop it, but you won't have enough time to hit Ganon afterward.

Instead, just hit Ganon after he stabs with the trident.

Second Phase

After you hit him enough times, he will roar.

This time, he will throw the trident at you. It will spin as it flies toward you. You can bind to the trident, but this will make Ganon disappear and reappear, so instead, hit Ganon while he is waiting for the trident to come back to him.

Sometimes he will spin the trident and make Fire Keese fly toward you. Move out of the way of each Fire Keese. If they hit you, you will be on fire and take damage for a few moments. If they hit the wall instead, they drop energy, so collect it to charge up your gauge.

Third Phase

After you hit him enough times, he roars again.

He will still send Fire Keese at you, so just dodge them as before.

This time, he will play Dead Man's Volley by sending out a fireball that slowly moves toward you. Switch to swordfighter form and hit the fireball back at him repeatedly until it hits him. He will be stunned. Run up to him and hit him repeatedly.

Fourth Phase

After you hit him enough times, he roars once more.

He will use a combination of his previous attacks, but this time his fireballs move more quickly toward you, and you will have to bounce it back more times before it hits him.

After the Battle

Afterward, there is a cutscene. Tri's level gauge will increase. If Tri reached level 5, certain monster echoes will require fewer triangles. You get 5 Might Crystals.

Pick up the Heart Container (or leave it there for more of a challenge), then talk to Tri at the glowing spot and leave the dungeon if you're ready. There will be a cutscene.

Before you leave the room, you can learn the Zelda's bed echo. Then exit the room and go west to the main hallway. Go north to reach the throne room. Go north and there will be a cutscene. This starts the next quest, Rescuing the Hero Link.