Upon entering this dungeon, go forward to the Bird Statue and save. You'll find the path ahead to be blocked by a large river of lava. You cannot run or jump across ... so you think. Look up and you'll find some plants hanging from above. Hit one with something (preferably the Hook Beetle, to save your ammo) and water will fall onto the lava below, temporarily solidifying and making a viable platform. Jump across quickly - it does eventually disappear.
On the other side, hit the next plant above the lava to make another platform. You can ride this one for a while longer, as it is in a current (although how that affects anything is unknown to me). Use your shield to block any arrows the Bokoblin Archers shoot at you, then, at the end of the current, jump onto the nearby solid platform. Go up the hill and finish off the monsters. Get rid of them all to find a chest and open up a doorway; the former will contain a Small Key.
Drop down from the ledge and you'll meet up with a Mogma, Guld. He'll give you some advice for the future, although you may have to write it down, because it could be a while. (Alternatively, read my FAQ.) Unlock the door nearby.
In the next room, utilize the nearby Bird Statue and head downstairs. As you do, defeat the Bokoblins and the Dark Keese, then go through the doorway. In this next room, go left to find a chest (Red Rupee), then go downstairs to a ledge looking over the room nearby. Drop down onto the metal grating blocking you from falling into the magma and immediately head for the rock. The enemy below, a Magmanos, will probably end up launching you to a higher ledge. There, get off of the rock and start ascending the vinery. Upon landing, defeat some more Bokoblin Archers, then continue along the vinery to another ledge. There, get rid of the other Bokoblins and drop down to the Bird Statue below. Use it and go through the door nearby.
In this room, you'll face a single Dark Lizalfos. The strategy to defeat it is the same as for a regular Lizalfos; it is merely stronger and can Curse you with its breath. Defeat it and grab your rewards, then go through the unused doorway.
Here, you'll find three Cursed Spumes in this room. Use the Bow to finish them off. North of where you entered the room, you'll find a statue's mouth clogged with rocks. Do a 180 to find a tunnel high in the wall. Send the Hook Beetle along it to find a few Rupees. When you get to the Bomb Flower patch (you may need to relaunch the Hook Beetle), grab a Bomb Flower and run into the rocks in the statue's mouth. This causes the lava to flow now. Use the Hook Beetle to knock the water out from one of the plants above the lava, then ride the platform to the ledge. There, disembark, defeat the Bokoblin Archers, and go through the only usable door.
Here, you'll find a Mogma being held captive above a pool of lava. After a short conversation, go around the room and you'll find some molten rock on the ground. Clear it with the Gust Bellows and you'll find some treasure, much like with sand. At the end of this path is a chest, inside which you'll find a Small Key. Exit the room, then go through the nearby locked door.
Here, you'll proceed forward by cutting down the plants and going further before the plants grow back (or you can just try weaving through them). Once you reach the fire blockade, go south to find some more water plants at the intersection. Open the chest to find a Red Rupee, and you'll also find a fairy in one of the pots. If you haven't refilled your Empty Bottle with anything useful, I suggest putting the fairy in it. Go up the nearby staircase and open the western treasure chest for a random treasure. Go to a water plant now and thrust your sword at it; this should leave the plant hanging on the sword. Go to the northern platform overlooking the fiery blockade. Lock-on to the frog statue and do a vertical slice to quench the statue's thirst.
Proceed forward here, defeating the Dark Keese and the Bokoblin. Use the Bird Statue on the way, then go through the doorway at the end of the path. In the next room, you'll need to defeat two Magmanos. Use one of the rock slabs in conjunction with a Magmanos to reach some water plants. Thrust one onto your sword and hit the ground. When one of the Magmanos reveals itself, throw the water plant at it and slice the now-solidified Magmanos until it shatters. Repeat this with the other one, thereby making the lava drain out of the room and revealing a door.
The captive Mogma from earlier will then call to you from his perch. Go through the newly-revealed door to find the pit above which he's hanging. Hit the nearby wall switch to lower the Mogma to the ground. After a short scene, open the chest to get the Mogma Mitts. They function like the Digging Mitts, but also allow you to dig and travel underground in certain areas. (It is differentiated from the "Dig" command by being named "Burrow".)
Try out the nearby patches of dirt. Generally, one of the holes with the larger opening after digging is a viable burrow area. Dig into the one nearby and learn the basics: the Control Stick makes you move, holding A makes you move faster, swinging the Wii Remote hits things (eg. destroys boulders, pushes along Bomb Flowers), and Z lets you see the above floor when applicable. Anyhow, go around here and collect a fair amount of Rupees. Hit the Bomb Flower to the north to get rid of the rubble, then go to the northeastern light to emerge aboveground.
In this new room, blow away the pilings of molten rock with your Gust Bellows to find some new dig spots. Use the nearby Bird Statue first, then dig around to another pathway. Here, go around to the west side of the central switch, then hit it to move the gate. Get aboveground and go to the doorway ahead, then upstairs to the eastern room.
In this room, go down the southern hallway and onto the floor switch to raise the bars for a future shortcut. Return to the broken northern bridge to find some Bokoblins. Shoot them down with the Bow, then hit the Clawshot targets. Be sure to hit the floor below as well -- you'll find some Blessed Butterflies with a Goddess Wall down here. When you're done, Clawshot to the above level, then continue to the next room.
Here, we find another captive Mogma. (As a species, they seem to be almost as bad as Princess Peach, eh?) Speak with him and go around the corner to the gate. Burrow into the nearby tunnel and you'll find two switches controlling the above gates. Hit the bottom, then the top switches and get out of the tunnel. Go around the corner to a water plant. Thrust it onto your sword and return to the fire gate. Lock-on to the frog statue and do a vertical slash to douse the flames.
Go into the room you just opened up and pull down the wall switch to give the Mogma some freedom. Go back and speak with him to eventually receive a chest; open it to receive the Dungeon Map.
Now, it seems there is a false wall nearby hiding a hidden room. In the room you most recently unlocked, Bomb the eastern wall to find a dig spot. Burrow and you'll find the tunnel passageway to it. There is a Moldorm around here. You hurt it by attacking its tail. If you are spotted, you are chased at a relatively high speed, although you can stun it by dodging at the last second and letting the Moldorm hit the wall. Anyhow, finish it off if you want, then leave via the western exit.
Here, you can open the chest to find a Small Key. Climb the vinery nearby to reach a ledge, then drop down and leave via the western door. Back here by the broken bridge, shoot down any Bokoblins that on the other side, then Clawshot over there. On the other side, don't go through the door. Instead, go south and press the floor switch. This creates a shortcut to where you fought the Dark Lizalfos from earlier. Go across that bridge into the east room.
Here, burrow into the spot next to the left gate. Go around to the right side of the gate to the switch. Smack it and return aboveground. Continue down the hallway and the stairway. At the water plants, thrust one onto your sword and stand on the floor switch to raise some bars, making another shortcut. Drop to the grating in the center, luring out the Magmanos, then solidifying and shattering it. This ends up draining the lava, much like before.
Follow the newly-revealed path down the hall to and through the doorway at the end. Here, go to the balcony to find a chest, inside which you'll find an Empty Bottle! Return inside and go down the hall. Climb onto the ledge across from you and go left, back along the path you opened up before. Go through the door by the Bird Statue. Head across the bridge, go to the right, and follow the path across the other bridge, then go through the door on the left.
Here again, go downstairs and use the Bird Statue. Unlock the door with the Small Key to go to a new area.
Here, go along the path to the river of lava below. From a distance, use your Bow to kill off the Cursed Spumes and the Bokoblin Archers atop the high western ledge. Use your Hook Beetle to hit the water plant above the magma. Jump across the newly-made temporal platform to find a door. Go through it.
In this room, go along the path and you'll soon reach a burrow spot and a gate. Burrow underground and go to the nearby switch. Smack it and you'll eventually get spotted by the nearby Mogma. The Mogma will re-smack the switch. Go around the corner and towards the Mogma, who responds by daring you to catch him. This part is simple -- wait for him at an intersection. As he approaches, dash out and touch him (touching him ends this).
Afterwards, you both will return aboveground and, after a conversation, you'll receive a chest. Open it up for a Piece of Heart and an opened gate. Go through the opening to find some Cursed Spume and Dark Keese. Get rid of them and then hit the water plant above the lava with your Hook Beetle. Ride the platform along the current and jump off at the other side. There, step onto the floor switch to create yet another shortcut, then save at the Bird Statue. THIS IS HIGHLY RECOMMENDED, BECAUSE THE NEXT FEW MOMENTS CAN SCREW UP REAL QUICK.
After saving, burrow into the nearby patch. Go around the tunnel, noting the locations of the Stamina Fruit as you do. Attack the boulders in the corner, then smack the Bomb Flower to the north and all hell breaks loose. That magma is now rushing towards you - if you touch it, you die. Dash around corner and continue dashing until your Stamina Gauge is a sliver from empty. Collect the first Stamina Fruit you find as you go -- the second is either too risky or already burnt. Don't let your Stamina Gauge empty; if it gets too low, just crawl along at the normal speed.
If you successfully exit these tunnels, the statue heads outside will start to spew out lava, creating a current in the below river. Save at the nearby Bird Statue, then go through the door nearby and downstairs. Go to the edge of the river, then launch your Hook Beetle above to the water plant. Hit it, then jump onto the platform.
At the other end, jump off the platform and head upstairs to a Bird Statue and an intersection. Use the former, and go the seemingly dead end behind the former. You'll find two statues below -- one looks likes it's sleeping, the other like it's awake. Drop down onto the one that is sleeping - it was the left one for me, and I don't know if it is randomized. Anyhow, you'll reach a magical platform.
Head along the path and around the corner to find a group of Blessed Butterflies. Summon up a Goddess Wall (if you need healing, I'd recommend drawing the Triforce or some hearts), then go through the door nearby. You need to defeat the two Dark Lizalfos here to unlock both of the doors. Do so and go through the unused one on the high ledge.
In this area, go upstairs to a kind of landing. Go around the bottom of the room and you should find another grouping of Blessed Butterflies nearby; you can also summon a Goddess Wall here. Proceed up the staircase, defeating the Dark Keese as you go. At the part with the vinery, look up to find two separate sections. Clawshot to the top-left section, then turn and go to the hidden set of vines near the ledge. Land on the ledge to find a random treasure within the treasure chest. From there, you can Clawshot to the right set of vines to continue your journey to the top of the stairs. There, go through the doorway to the next room.
Here, you'll find five statues, each having some wings. Imagine the wing numbers as the statue's own number (0, 1, 2, 3, 4). Memorize their positions and burrow underground. Here, you'll need to travel onto the switches beneath the statues in their numbered order by wing number. After the first two, you need to smack the Bomb Flower to the north to continue with the sequence. Once you end up hitting them all correctly, you'll have to defeat a Moldorm.
Once you defeat the Moldorm, you can return aboveground. Here, go to the chest to find the boss key for this dungeon, the Mysterious Crystals. Go up the stairway at the other side of the room and outside via the doorway. There, step onto the floor switch to open up the barred gate. Go along the path to the intersection from earlier and save at the Bird Statue.
Go up the northern staircase to the large door. Examine the door and properly place the Mysterious Crystals into the lock to unlock the door, which starts up your next boss fight.
Demon Lord Ghirahim
In the initial part of the battle, Ghirahim will simply walk towards you. He comes with one hand raised upward, glowing red. The purpose of this is to grab your sword when you slice at him. If he DOES grab your sword, do a down-up vertical slice, or he'll steal the sword. During this time, he also can slap you if you take too long to hit. Additionally, you'll probably notice the red projectiles near him. If he grabs the sword and/or you take too long to hit him or get back your sword, they will hit you.
How do you hit him? Well, you need to lead his hand in one way, then quickly swing in a different way. If you DO manage to hit him, be sure to hit multiple times, since he will be very temporarily stunned by the initial hit. After taking a hit, he'll also send some of the red projectiles at you -- shield bash them or use the sword block, like in the last battle.
During this time, if he does manage to steal away your sword, you have two options. You can run around until he throws your sword at you, at which point you can grab it, or you can shield bash him during a slash.
Continue attacking for a while, after which it'll change a bit.
In the second half of the battle, Ghirahim will use his two swords and | | will use three attacks. One involves teleporting and slashing at you (kind | | of like Sephiroth in Kingdom Hearts). Another involves a running tackle and slash combo, and another has Ghirahim surrounding you with red projectiles. Another has him doing a nosedive onto you -- you can only run around to avoid this, although you can get a few hits in when he lands. He also has a (usually) counterattack whenever you hit his swords rather than him when he holds them up in those configurations.
For the first attack, just jump around, preferably backwards (because he'll appear from behind, and his position is apparently determined upon actually teleporting). For the second, shield bash Ghirahim to stun him and get a few hits in, or swing at him on the side his sword isn't on. As for the third, execute a spin attack that will hit all of the projectiles.
At the end of the battle, grab the Heart Container and go through the opposite doorway. Here, walk up to the altar and hit the crest with a Skyward Strike. You then will proceed to purify your sword with Din's Flame, which transforms it into the legendary Master Sword, the blade of evil's bane! You can now utilize the Gate of Time within the Sealed Grounds. After the scene, you will end up outside the Fire Sanctuary.