After meeting Melari on Mt. Crenel, you continue on to the second dungeon, the Cave of Flames.
Explore the Cave
First, go through the door to the right. The bomb enemies in here will shoot around the room if you hit them with your sword, and will explode if they hit you. The safest way to beat them is to draw them in with the gust jar and shoot them out. If you have the boomerang already, hit them with that and they explode at a distance. Once they're gone, bomb the north wall, and go through.
To beat the monsters with the shells, get out your shield and have them bump into you with it raised (be SURE to press the button to raise the shield!) Once they're on their backs they're vulnerable, so hack away. Grab the chest that appears for the compass, and exit through the door that opened.
One of the rupees is actually a Like Like in hiding. Don't walk right up to the rupee, instead, you can collect them by hitting them with your sword (you can collect other items this way too). When you do that the Like Like will be revealed from a safer distance. Kill the Like Like, get any rupees you missed, and go down the stairs.
There's only one way you can go, so follow the path beating monsters until it splits two ways. Go right and into the room, and hop into the mine cart for a ride. When you're done, continue on the path until you reach a bombable wall, and bomb it.
Use the gust jar to take the armor off the enemies, and a shrinking portal will appear. Use it and go through the small hole in the northeast part of the wall. Keep going right and you reach another small hole, go through. Take the hole through the south wall and continue south to the next room.
Head left and down, and there's a tiny gap in the stones that you can jump down, so jump. Avoid the flames to reach the shrinking portal to the right. Use it to grow to normal size, and use your sword to slash the flames away (and kill the chuchus). Go up the stairs and grab the map from the chest. Go down and left (the blocks in the lava will crumble so don't stand on one too long) and get the chest for a blue Kinstone piece. Step on the switch below to open the door. Make your way around to the door you just opened (you can get rid of the pots in your way with the gust jar) and go through.
Ride the platform to the other side and get off quickly so the platform doesn't crumble under you. The wormy enemies here will roll into a ball when hit. You can then pick up the ball and throw it, and your goal is to throw a ball into the holes in this area. The only two holes you need to worry about are the one below the chest (50 rupees) and the one below the pot to the north. You may want to fill the other holes too to get the wormy guys out of the way. Once the hole up north is filled, get rid of the pots and go up the stairs.
Below is a tornado, so jump into it and head south to the next one. After getting that second boost, go right and start floating north. When you're over the ground you can hit R to drop. Go up the stairs. First, step on the switch (it's in the corner) to open the door. There's a block sticking out from the rest, push it up. Then push the pillar with the chest on it to the left until it drops into the hole, letting you reach the chest. Get the small key from inside. Exit north through the door you opened.
Take the path east until you reach the mine cart, and get in. At the end, use your key on the nearby door and go through. Walk along the tracks to reach a lever, hit it with your sword to switch it and change the tracks. Now return to the cart and ride it to a new area.
In the room to the left are the spiky monsters, so get out your shield and defeat them. Exit north. You can drop in the hole here and the traps will go over your head. Once they go away, go forward to jump out of the hole. The mine cart here is upside-down so you can't use it. Walk over the tracks to the right, and when you see the pots below, get rid of them and bomb the wall there. Go through and grab the piece of heart, then return to the previous room. Exit north.
Jump down and you'll be attacked. These chuchus turn spiky so you can't hurt them, but sometimes they let down their guard and you can hit them. You can also use bombs against them. Once they're gone, a chest appears containing the Cane of Pacci. All it does is flip stuff over, which is useful for the mine cart from earlier in the dungeon. It has other uses in this dungeon, and outside of it can be used to flip over pots in houses to reveal a shrinking portal, giving you access to new areas. Exit west.
There are lava platforms here, but one is spiky. While standing on the first lava platform, use the Cane of Pacci on the spiky one and it will flip over so you can walk on it. Go across. Ezlo will tell you to use the Cane of Pacci on the hole below, so do it. A spark will appear in it, and when you get in, it shoots you in the air. If you're facing the upper level while in the hole, it will shoot you up there, so do it. Step on the switch to reveal a blue warp and open the door, go through it.
Use the Cane of Pacci on the mine cart to flip it over, and get in. When it lets you out, push the pillar with the chest on it into the hole, and grab the small key from inside the chest. Ride the cart back to where you came from, and go back to the room to the north. Drop down below and use the key on the door above. Head down the stairs.
To the right is a shrinking portal, use it and carefully get past the traps. If you're walking you can hit R to roll, which gets you out of the trap's way faster. Go through the small hole. Go through the maze area to reach a shrinking portal, use it to grow to normal size. Now, when you go back through the maze, the small red things will activate and move down the path, hurting you if you're in the way. Move quickly and move to the side to keep out of harm's way. Once out of the maze, flip over the mine cart and get in. At the other end, flip the switch to change the tracks and get back in the cart to get to a new area.
DON'T put one of the worms into the hole at the top left. You need all four worms to go into the four holes at the bottom right of the screen so you can pull the pillar with the switch on it, and push it into the top left hole. Once it's in there, hit it and the path will open. Continue on.
In the next area, drop off from the north end of the ledge, get the chest (blue Kinstone piece) and push the top block out of the way. Go a little south and you see a hole, use the Cane of Pacci to power it up, and jump in to get to the ledge with the chest (green Kinstone piece). Exit right.
Slash the flames out of the way, then get in a position so the first lava platform is not in your way and you have a clear shot to the spiky one. When the spiky one passes, flip it with the cane. You want to ride the platform UP not down, so wait until it's coming up from below to get onto it. Get off at the upper right (below where the big door is). Step on the switch here to create a red warp. Next, go back left, use the Cane of Pacci on the spiky platform again, and head left across the platforms to reach the start area.
Flip over the spiky platform a third time, and this time, ride the second platform down. Quickly flip the platform below to get on, and do the same for the one to the right. Get off at the other end. Go up, and before moving on, use the cane to flip all the pots to the right to get them out of the way. Then flip the moving platform above you, hop on, then get off onto the safe area below. Flip the other platform above, and get on. You have some platforms to flip, so don't waste time and flip them as soon as you can. Make your way to the right, and at the other end exit to the next area.
Go up the stairs and drop down into the hole. If you want a green Kinstone piece head right first. Carefully avoid the traps to reach the chest with the piece inside. Avoid them again to exit left. Use the cane on the top hole to boost yourself up to the ledge, and drop down the other side. Use the cane on this hole, and get in and face the tornado so you float up to the ledge above. Take the path right to the next room.
At the end you reach another tornado, and if you look on the floor below there's a path of tiles. Follow that path as you float to get to the other ledge. Once you reach the lava room, you have a lot of tornadoes to navigate through. Avoiding the stalagmites, use the one at the starting ledge and head south to a safe spot. There's another tornado here, and before moving on you may want to use it (using the cane to reach it) to get to the chest on the ledge above, it contains 100 rupees. Next use that tornado to float slightly northwest to the spot with the flames and the hole. Use the cane here to get to the ledge above. Next is another tornado, use it to go in a general west direction, using tornadoes on the way to keep going. Stop at the platform to the lower left with the chest on it and grab the green Kinstone piece. Then use the cane to reach the next tornado, and go into the next tornado northeast to reach the ledge with a big chest on it (big key). Drop off the platform to the north (left of the chest). Slash the flames for recovery hearts if you need to. Flip over the moving platform to the left, then as it's going up, take it up to the boss door.
To get to the boss room you have to drop down the hole. First use any pots to recover hearts if necessary.
Gleerok will spit flames, but they can be cut with your sword, and sometimes hold recovery hearts. You need to circle the lava pit so you're around the side of Gleerok (you should roll to move faster) to use the Cane of Pacci on its shell. When you hit it and it's stunned, run across its neck and hit the spot on its back repeatedly. When Gleerok starts to sink, quickly run back across its neck so you don't fall in the lava, and stay near the wall, as the lava will spread outward. Be careful not to get hit by any falling stones. Stay out of the way of Gleerok's mouth, it will do a big flame attack (you can still cut down the flames). Repeat until Gleerok is beat.
The heart container and warp tile are above.
After this dungeon, you should infuse the Picori Blade with the two elements that you obtained.