After you restore the Mirror of Twilight, you can go through the portal to reach the Palace of Twilight.
Get a Key
If you need to leave the palace, step on the glowing symbol and press A.
When you approach the area ahead, Midna will comment on the Twili there. You can't talk to them.
The north path is blocked, and one of the side paths is broken, so go along the other path. You will find a door there. Go through.
Make your way north, killing Shadow Keese and Shadow Deku Babas. Near the north end of the room, a Zant Mask will appear and spit orbs of dark energy at you. Use the Shield Bash to knock the orbs back at the Mask, then kill it with your sword. A chest will appear. Open it to get a Small Key.
Get a Second Key, and the Compass
Use the Clawshot on one of the targets on the north wall, and go through the locked door in the north wall.
Walk into the dark fog down below and you will be turned into Wolf Link. After some reassuring words from Midna, use your senses to see the path out of the fog to the north. Transform into a human and use your shield to knock the energy orb back at the Mask. Then run into the fog, where you will become a wolf again, and use a charged attack to hit the mask. Repeat this to kill the Zant Mask.
Two chests appear after the Mask dies. Shadow Vermin will appear in certain areas of the room as well, so be ready to spin attack or charge attack them. Open the southern chest to get the Compass, and open the northern one to get a key.
Go to the Mini-Boss
Don't go through the north door yet. Instead, look for a clawshot target on the ceiling above a high ledge to the side. Use the wall target near the ceiling target to get close enough to use the ceiling target, then drop down to the ledge. Kill the two Shadow Deku Babas, and open the chest.
Then use the Clawshot targets to reach the north door. Go through.
After a cutscene, go north and approach the hand. Phantom Zant will appear, and summon a lot of monsters. Kill them all, then run up to Phantom Zant. He will keep disappearing and reappearing, so keep going after him until he stays long enough for you to hit him with your sword. If you wait too long, he will summon more Shadow monsters.
After you hit him enough times, he will disappear and put fog in the middle of the room, ending the battle.
Get a Piece of Heart
Approach the hand to the north, and Midna will ask you to take the orb, known as a Sol, to the entrance. Hit the hand and pick up the Sol, then walk into the fog in the middle, and the Sol will clear away the fog. Keep going south and the hand will float upward. Approach the small round pit in the floor until the "Place" button appears on screen. Place the Sol in the pit, go up the stairs that appear, and defeat the enemies that attack. The hand will approach the Sol. Go south until you are at the top of the stairs, then try to use the Clawshot on the Sol before the hand can pick it up. If the hand takes it, stun the hand with the Clawshot or some arrows. If the Sol gets too far away for you to use the Clawshot on it from the southern ledge, you will have to go back down and put it in the hole in the floor to recreate the stairs and try again.
Once you have the Sol and are on the southern ledge, go south through the door.
Go south and the hand will appear through the wall. Go south into the fog. Shadow Vermin will attack. Find the pit in the fog that you can place the Sol in, then go up the stairs that appear. Stun the hand with the Clawshot as needed, then when you are past the stairs, grab the Sol with the Clawshot.
Take the Sol south, throwing it onto the higher ledges. Carry the Sol to the end of the platform to the south, and jump down with it. Go through the door.
Go south and the hand will appear through the wall again. Look at the map to see a treasure chest in a side path. Take the Sol there, being careful to avoid the Shadow Baba, and you can go through the waterfall of fog. Use the Clawshot on the target on the wall above the chest, and open the chest to get a Piece of Heart.
Place the Sol
Go back down and pick up the Sol, and carry it south, going past all the monsters, and go through the southern door.
There will be a cutscene where the Twili near the door is transformed back to normal. Take the Sol around to the other Twili in the area to turn them back to normal.
Take the Sol to the large circle in the center of this area and put the Sol into one of the pits. Midna will say that you need to find the other Sol.
Get a Third Key
Step onto the green square that appeared nearby when you placed the Sol into the pit. The platform will take you across the gap on the side. Go through the door there.
Kill the nearby keese, then go north to the lower area. Use the Clawshot on one of the wall targets, then use it on the ceiling target. Lower yourself down onto the moving platform. When the platform reaches the area to the north, jump across the gap. A Zant Mask will appear. Use your shield to knock its orbs back. Make your way north across the moving platforms. When you reach the area to the north, kill the Zant Mask. If the Zant Mask is too far away, go to the north door and wait for the Zant Mask to appear in a closer spot where you can hit it. After the Zant Mask dies, a chest will appear. Open it to get a key. The other chest here contains a purple rupee.
Go through the locked door to the north.
Get the Dungeon Map, and a Fourth Key
Go north and you will encounter three Shadow Beasts. Kill them as before, making sure not to leave only one of them alive. After they are gone, a Zant Mask will attack. Kill it, then three Zant Masks appear in the fog. Kill them with a charged attack. A chest will appear. Go north and transform into a human, then use the Clawshot on a target on the north wall. From there, look up to see more Clawshot targets on the walls and ceiling. Use the Clawshots to reach all of the chests marked on the map in these upper areas. One of the chests contains the Dungeon Map, and another contains a small key.
Use the key to go through the north door.
Get a Second Piece of Heart
Go north and another Phantom Zant will attack. Kill it the same way as before. Afterward, hit the hand in the north wall with your sword, pick up the Sol, and place it in the pit in the fog. Kill all the Shadow Vermin and the Shadow Beast (which is by itself, so no need to look for others), then you might want to pick up the Sol and take it to a northern corner of the room to lure the hand away from the center of the room. Afterward, put the Sol in the pit in the floor and quickly go up the steps, and use the Clawshot to get the Sol before the hand can pick it up. Go through the southern door.
Go south and the hand will appear through the wall. Go south into the fog and put the Sol into the pit. Kill the Shadow Keese and the Shadow Beast. You can remove the Sol from the pit to make the stairs go back down, then put it into the pit and quickly run north so you are lifted up when the stairs go up. Then go up the stairs to the highest level, and use the Clawshot to get the Sol. From there, go south and through the door.
Go south and the hand will appear through the wall once more. Go south into the fog, and find a dark orb at the north side. Lure the hand away if it is close, then stand to the left or right of the dark orb to charge it up and make a glowing platform appear beneath you. The hand is slow enough that if you lured it away, it won't be quick enough to land on you before the platform moves you out of the way. Wait for the platform to go south and rise up to a niche in the wall. Throw the Sol into the niche, then jump into the niche and open the chest. Then pick up the Sol and go back to the dark orb, luring the hand away if necessary. Stand on the other glowing platform this time, to reach the chest on the other side from the one you just got. One chest contains a Piece of Heart, and the other contains a purple rupee.
Get a Fifth Key
Go back to the dark orb and stand near it to light it up and be lifted by a platform, but this time, go to the ledge at the north end of the room to lure the hand there, then move onto one of the platforms that goes across the middle of the room. Make your way along these platforms to reach the raised area that has two dark orbs on it. Stand between the orbs to make a new platform rise up beneath you. Stay on it and set down the Sol to kill the Keese with arrows when they are close enough to lock onto, then pick up the Sol and go through the south door.
Ride the glowing platform to the middle, and place the Sol in the other pit. There will be a cutscene.
Go north and kill the Shadow Kargaroks, then stand on the red symbol on the ground and do a spin attack to temporarily dispel the dark fog. Jump over the gap and go through the north door.
Go north, killing Shadow Keese and Shadow Vermin. Swing your sword to temporarily remove the dark fog. Get rid of the fog to reveal two pits in the floor where orbs can be placed. Go north, kill the Shadow Deku Baba, and pick up each of the orbs and put them into the pits. Stairs will appear. Go up, kill any Shadow Keese nearby, and hit the dark orb with your sword. Stand on the glowing square and ride the platform to the other side of the room.
Kill the Shadow Deku Baba, then go south and three Zant Masks will appear. Your sword is stronger against them, so just hit them with your sword to destroy them. Open the chest that appears. It contains a small key.
Stand in the middle of the three dark orbs and do a spin attack to light up all three at once. The platform will go past some Shadow Keese up above and will take you to a locked door. Go through.
Get a Sixth Key
Kill the many Shadow Kargaroks in this area. There is also a Shadow Beast here. Afterward, stand between the two dark orbs and do a spin attack to light both of them up. Ride the platform to the southern area. Kill the Zant Mask. More Zant Masks will appear, but you can't reach them from here, so do a spin attack at the two dark orbs here to create a platform to return to the previous area. Kill the Zant Masks there, then open the chest to get a small key.
Get the Big Key
Then use a spin attack on the waterfall of dark fog and jump over the gap. Kill the Shadow Kargaroks, then look up to find a Clawshot target. Use the Clawshot on it, and make your way up to the top, where you find the chest that contains the Big Key.
Get a Seventh Key
Make your way back down the ledges, then use a spin attack to cut through the dark fog, jump over the gap, and go through the locked door.
Go toward the fog up ahead, and Shadow Beasts will appear. Kill them as you have done before, making sure not to leave only one alive. If you can get them close to each other, you can get rid of them with a single spin attack.
Afterward, cut through the fog up ahead, and do a spin attack while standing in the middle of the dark orbs. The platform will raise you up, and four new platforms will appear. If you stay too long on the center platform, it will disappear and you will have to do another spin attack to make the platform reappear.
Turn to face the door, and jump onto the platform in that direction. Then two platforms will appear. Jump on the one that is farther away from the door. It will go upward. Continue facing the door, and you will see a ledge at the top. Jump onto it, kill the Shadow Deku Baba, then jump onto the next platform. It will take you toward a wall. Face that wall, and use the Clawshot on the target on that wall. Kill the Zant Mask, then use the Clawshot on the target in the ceiling and lower yourself onto the platform below. Turn to face the wall that the platform is moving toward, and use your Clawshot on the target on that wall. Kill the Zant Mask there to make a chest appear. Open it to get a small key.
Jump onto the new platform that appeared nearby. It will take you to a locked door. Go through it.
Go to the Boss
Go forward and kill a Shadow Beast, then go forward and kill two more. Then a wall will appear around you, and two more Shadow Beasts will appear. Kill them simultaneously. Repeat this when another two, then four, then another four appear. Then the wall will disappear. Go through the boss door.
Usurper King: Zant
Go forward into the room. After the cutscene, the battle begins.
Phase 1: Forest Temple
Run to the side to avoid the orbs, then use the Gale Boomerang on him to knock him down. Hit him with your sword when he bounces near you. Repeat this until the next phase.
Phase 2: Goron Mines
Use the iron boots to avoid getting knocked off. Block the orbs with your shield. When he slumps forward after shooting orbs at you, take off the iron boots and hit him with your sword. Repeat this until the next phase.
Phase 3: Lakebed Temple
Equip the Zora Armor and Iron Boots. When Zant appears in the mouth of a mask, use your shield to block the orbs, then use your Clawshot to pull him out and hit him with your sword. After the mask goes back underground, walk forward and stand in the middle of the pit. Then, four masks will appear. Look for Zant when the mouths open, block the orbs if necessary, and use your Clawshot on him to pull him out and hit him with your sword.
Phase 4: Forest Temple
Switch back into your regular armor and remove the Iron Boots. Dodge the orb attack, and dash into Zant's pillar twice to knock him off, then hit him with your sword. Repeat this until the next phase.
Phase 5: Snowpeak Ruins
Watch Zant's reflection in the ice and roll away when he is about to land, or try to be between his feet when he lands. Lock onto a foot and use the Ball and Chain on it, chase him as he stomps around and starts shrinking, then hit him repeatedly with your sword when you are close enough. Repeat this until the next phase.
Phase 6: Hyrule Field
When Zant is slashing with his swords, stab at him or use the Back Slice to hit him. When he spins very quickly, do your best to dodge or deflect with your shield, then when he slows down and slumps forward, hit him with your sword.
To Hyrule Castle
After the battle, go up to the throne and take the Heart Container, then approach Midna to return to the outside of the Palace of Twilight. Approach the portal, stand on the gold symbol in front of it, and press A to go back to the Mirror Chamber.
If you are ready for the final dungeon, warp to Hyrule Castle Town and go north toward the castle. After a cutscene, the barrier around the castle will be gone. When you are ready, go north and walk up to the door, grab the door handle, and push to enter Hyrule Castle.