This part will get you through the entire Earth Temple.
With Medli on board the King of Red Lions, let's get underway. Warp to Outset Island and sail east one block to Headstone Island. Before going there, if you have ten Knight's Crests (you should have ten at this point), you may want to stop at Outset Island to visit Orca and present him with the Knight's Crests. He will then teach us a new sword technique that he and his brother have tried for years to perfect -- the Hurricane Spin. It is similar in technique to the simple spin attack, but you hold down the B button until your sword lights up, and then Link will whirl around the room spinning incredibly fast, slashing anything that touches his sword in the process. The downside is that Link will be temporarily disoriented at the end of using the Hurricane Spin. Orca will be so happy that Link has learned this technique, he will gush out tears of joy from his eyes.
Once you reach Headstone Island, the King of Red Lions will tell Link that if he needs Medli to do something, use the Command Melody to control her. Upon entering, play the Earth God's Lyric before the giant stone tablet. Medli will quietly play her harp, and the giant stone tablet will crack and crumble, opening the way to the Earth Temple. The both of them will automatically drop down the hole in the next room and enter.
Inside the Earth Temple
Our first action is to go over to the door ahead of us that's on a ledge, and to do that we need to carry Medli and leap off the ledge we're on so she can fly us over there. To have Medli fly, press the A button repeatedly to flap her wings. However, when flying her solo, you can only keep her airborne for a certain amount of time before she drops to the ground or until she gets hit by an enemy. Keep carrying Medli with you as you go through the door, which is what we'll have to do to get through the rooms of this dungeon except at certain points because Medli will stay in whatever room you happen to leave her in. Leave Medli at the door in the next room and go to the right to take down the Moblins, then go up the stairs to your left and take out the Moblin there. Carry Medli with you up the stairs and then have her fly you to the top of the pillar straight ahead of you where there's a floor button. Put her down and use the Command Melody to fly her over to the top of the other pillar with the floor button. With Medli and Link standing on the floor buttons, the metal bars in front of the door below them will be raised. Have Medli meet Link near the door before resuming control of Link so he can carry her into the next room.
Here we have a closed-door battle with some Chuchus, which you can easily slay. However, there will be Purple Chuchus that you can't easily slay with the sword. Use the Command Melody to take control of Medli when you have only the Purple Chuchus left and have her stand in the beam of light. When she does, the green action button icon on the screen will flash, so press A button and she will move her harp around to reflect the beam of light onto the Purple Chuchus. This will turn them to stone, which will allow Link to smash them with the Skull Hammer when you resume control of him. (You can also wait for the Purple Chuchus to approach the light so they will turn to stone without using Medli, then smash them with the Hammer.) This will raise the metal bars on both doors. Bomb the teleportation pot in this room to open it, then have Medli shine a beam of light toward a raised section of the floor, causing a treasure chest to appear which contains the Dungeon Map. Take Medli with you as you leave this room through the other door.
In the next room we enter, there's a giant stone face with two jeweled eyes that sits above an area filled with a strange blue mist that affects Link's ability to use his weapons. There are two beams of light that shine into this room, and Medli can shine a beam into one of the eyes, but we need to find something else to shine the other beam into the other eye. First of all, have Medli stand in the beam of light to the right of the stone face and shine some light straight ahead toward the wall to the right of the face. This will clear away some of the mist to reveal a peg that Link must smash with the Hammer. This will raise the bars in front of a door close to the beam of light where Medli is now.
Pick Medli up and carry her through the door into the next room where there are crypts that will open and release some Fire Bubbles for you to take down. Climb up the ladder to where there's a big stone block on the ledge and pull it towards you, causing a beam of light to shine into the room. Then have Medli stand in the beam to shine light toward a raised section of the floor where we see a cloaked treasure chest to uncloak it. Open the chest to get a small key. However, this will cause creepy black portals with hands coming out of them called Floor Masters to appear, and if any of these gets a hold of Medli, she will be taken to a prison back in the room with the stone face that you'll have to fly her out of. Also don't let them get a hold of Link, because they will take him a few rooms or so back the way he came. To get rid of the Floor Masters quickly, use the Ice Arrow to freeze them and then smash them with the Hammer before they break free.
Go back to the room with the stone face, fly Medli out of the prison if she was captured, then carry her as you head for the locked door in the room. Beyond the door is a room with two floor buttons and some Chuchus to harass you, including the new purple ones. Slay all the Chuchus that you can slay, then aim a Fire Arrow at the closed windows to open one that shines a beam of light into the room. Lure the Purple Chuchus into the beam of light to turn them to stone, then place each of them on the floor buttons to make stairs appear toward the other door. Quickly go up the stairs before the Chuchus de-petrify and push the big stone block off the ledge, causing metal bars in front of the door to be raised. Then stand near the door and fly Medli over to where you are so you can carry her into the next room.
In there, slay the Floor Master, then push a big stone block toward the wall to open a hatch in the ceiling to make light shine into the room. Then have Medli stand in the beam of light so she can reflect it on two sun marks on the wall, creating an opening from which a statue on top of a block can be pulled out. Shine some light on the two statues sitting on the blocks to get rid of them, then on two sun marks on the opposite side wall so you'll have access to a teleportation pot that is already open. Push one of the stone blocks near the high ledge to raise the bars in front of the door on the ledge, and push the other block toward the wall to make a treasure chest appear, where you'll get the Compass. Climb up to the ledge to get it, then have Medli join you to flying her up to the ledge to carry her through the door.
Go up the stairs into the next room where you'll deal with Moblins and ghostly beings called Poes, which are only tangible when exposed to sunlight. They can enter into Link and possess him, causing his controls to be reversed for a while, but after that they will disappear. When the room is clear of enemies, another set of stairs will appear. You can leave Medli in there for now and go up the stairs through the door on your left. In that room, leap down and run near each of the crypts to make them open one by one, revealing in three of them life-sucking ReDeads that will stun Link for a while if they are facing him. Strike them down quickly before they latch onto you. In the fifth crypt there will be a small key to collect. Climb up the ladder that drops down so you can get out of this room.
Back in the other room, go to the locked door at the top of the staircase and open it. You'll enter a room where you'll get into a closed-door battle with a Stalfos, which will spin around swinging its spiked club at you. Use Bombs to blow up its body, then take your Hammer and smash its skull before its body reforms. After he is destroyed, two more Stalfoses will emerge from crypts to join the fun. Defeat them the same way you did the other Stalfos, and a staircase will now appear so you can open the treasure chest and get your next useful item -- the Mirror Shield. This will reflect beams of light like Medli's harp when Link stands in a beam of light. Make sure Link's sword is drawn so that you can use the shield to reflect light.
A beam of light will now shine into the room. Have Link stand in it and reflect the beam onto a moon symbol on top of the door. This will raise the metal bars so that you can now exit the room.
Back in the room where you left Medli, the Moblins and Poes will reappear. Take them down quickly, then have Medli fly up to a ledge where a beam of light shines on so she can reflect light toward some statues that are hiding a treasure chest and then angle the reflection down toward the ground. Link can climb up to the treasure chest to get a Joy Pendant. Have him stand where the light is reflected so he can aim the reflection toward a sun mark on the wall below where Medli is. This will open up a passageway for you and Medli to go through. Carry her through there to where a beam of light shines, then have Medli reflect light unto a statue to destroy it. Keep her locked in that direction while Link uses his shield to reflect the light toward a sun mark, revealing a hidden place where you can collect rupees. Take her through the door which leads back into the room with the stone face and fly them both down to the ground. Set up Medli under one beam of light so that she shines a beam into one of the eyes, then lock her in place and have Link shine the other beam of light into the other eye. The stone face will now turn into a glowing sun with spinning rays, the blue mist will disappear around the floor near it, and a staircase will appear to a door below it. Bring Medli with you as you descend down to the next floor.
Go down the winding stairs to a bridge where you see Blue Bubbles flying around. These will also affect Link with the same strange mist that will make him unable to use his weapons. Take them down using the arrows before slaying them with the sword. Then bring Medli over to a large stone tablet similar to the one at the entrance of the Earth Temple and play the Earth God's Lyric. She will quietly play the tune to make the tablet crumble, revealing a door behind it. In the next room, slay the ReDeads, then stand in the beam of light to shine it on the statue in front of you to destroy it. Also reflect the light into two giant mirrors in the room to make two other statues crumble, revealing two other doors. Leave Medli in this room and go to the door on your right. This will take you through a maze of blue mist and Floor Masters that you need to navigate carefully through to reach a treasure chest with a small key. Once you do, the blue mist will disappear, leaving you only with the Floor Masters. Avoid them and head back to the room you were in, going this time through the door on the left from the entrance.
Here there's a passageway that's partly filled with blue mist where Floor Masters are hiding. Blow away the mist with your Deku Leaf so you can see the Floor Masters and target them with Ice Arrows to stop them dead (you'll need to hit them twice with that weapon to do that). Then go across the blue mist to the other side where you see a peg that you must smash down with the Hammer. This will open up a hatch from which a beam of light shines. Move the giant mirror along its track so that it's under the beam of light to reflect it. Then cross back through the blue mist to go back into the room where you left Medli. In there, push the big stone block toward the ledge where there's a door, then have Medli fly up to the ledge to join you so you can carry her through the door that you can now unlock.
In the next room, watch out for Poes and Bubbles that will attack you unaware. Use the Mirror Shield to reflect the light shining into the room to make the Poes tangible so you can slay them. When they are disposed of, have Medli stand in the beam and reflect the light between the two large statues. Then have Link reflect that light onto the large statue to the right of the other two. This will reveal a door to take Medli through that leads to a maze of hallways where there's crypts lining the walls, and running past them will cause them to open, revealing enemies like ReDeads and Stalfoses. Go forward all the way to the end of the first hallway and go to the right where there's a treasure chest with 20 rupees in it. Then go back towards the door and this time go down the hallway to your first right and take a left until you reach another large stone tablet to bring Medli over to and play the Earth God's Lyric. This will reveal a door to a staircase leading down to a large chamber where, across from us, we can see the Big Key Door where the dungeon boss' chamber is. Now we need to get the Big Key to open that door.
First go over to the teleportation pot on your right to blow it open with a bomb. Then go to your left down the winding stairs until you can't go down any further them. Use the vines on the side of the wall to climb up, to the right, and then down a long shaft to the other half of the staircase near the bottom. Have Medli join you once you reach the door at the bottom of the staircase. Past the door you'll enter a room with another stone face that we need to shine light into its eyes. First off, fly Medli over to the top of the big structure in the center of the room to step on a floor button to make a beam of light shine into the room. Then have Link drop down and pull the first large mirror that he can to the end of its track. In fact, most of what we're going to be doing is finding large mirrors and pulling them to the ends of their tracks, some of which will require some fancy redirecting of light to open up walls that some of the mirrors are hiding behind. Once all the mirrors are in place, have Medli stand on top of one pedestal near the stone face to shine light into one of its eyes, then lock her in place and have Link shine light into the other eye. The stone face will turn into a shining sun, causing a staircase to appear below it that goes to a door. Go through that door as Link alone, and here in this room is a closed-door battle with a Darknut and some Blue Bubbles. Defeat them, and the metal bar in front of the door behind us will be raised, and a gate will open to a treasure chest which contains the Big Key.
Go back to the room with the mirrors where you left Medli and take her back to the big staircase chamber, having her fly up to the top of the stairs before having Link do the ardurous climb up the vines. Then pick up Medli and fly straight across to the ledge where the Big Key Door is located. Smash whatever pots you need to smash for hearts and a fairy, then open the door to meet the dungeon boss.
Earth Temple Boss: Jalhalla
Medli will stay outside the chamber while Link goes inside. After he does, he sees a dozen or so Poes dancing around before they notice him and start running into a giant mask in the center of the chamber. Then a giant obese Poe with a lantern will form from the mask. This is the dungeon boss Jalhalla. His attacks will include sucking you toward him with air, breathing out fire at you, and even landing on you with a belly flop, cursing you for a brief bit to run into the spikes along the walls of the room.
Although intangible, Jalhalla's weakness is light. Stand under a beam of light that shines into the room and use the Mirror Shield to reflect a beam of light unto him. He will then become tangible and fall down to the floor. Pick him up and toss him into one of the spiked pillars lining the walls of the room. He will break into multiple Poes that you must strike with the sword as quickly as possible before they merge together and Jalhalla reforms -- even if there's only one Poe left! (If you have the Hurricane Spin, charge it up before Jalhalla hits the pillar and let it loose after he explodes to strike many Poes quickly.) With each reforming, the light beam will shift around faster, and Jalhalla will be tougher to beat. When the last Poe is struck down, Jalhalla's mask will try to flee by floating to the ceiling, but a beam of light will cause it to fall to the floor and be smashed, turning into a Heart Container as Link dances with joy for defeating him.
After collecting the Heart Container and stepping into the blue light in the middle of the Triforce symbol, Medli will come into the chamber, and Link will place the Master Sword in the blue light before conducting her in playing the Earth God's Lyric. The spirit of Laruto will join Medli as she plays. After the song is over, Link will pick up the Master Sword, and its handle will suddenly change shape and its blade will sparkle. We've just restored the Master Sword's former power, but it's not yet fully restored. Medli says we should go find the other sage while she stays behind in the Earth Temple to continue praying, and she also asks Link to watch Prince Komali for her. He agrees before he steps into the blue light and vanishes from the temple.