As you enter the room, you’ll probably notice the ornate blue chest on the opposite side of the room. There is just one problem - you’ll fight two Blue Bubbles and a Darknut to get to it. The Blue Bubbles are easy to get rid of; just use the Deku Leaf or an Ice Arrow then attack.
The Darknut is the same as ever. Just parry until the armor on the torso is gone, then attack! After the enemies are dead, the gate blocking the Boss Key chest rises. Open the chest to get the key, then return to the previous room.
Back in the mirror puzzle room, it may please you to know that you are able to get Treasure Chart #20 now. If you wish to get it, go through the door at the end of the secret passage you opened earlier. Don’t bother bringing Medli with you. If you do not wish to grab the Chart, skip the next paragraph.
In this room, you’ll find it is like the room where you first encountered your first three Redeads. The half of the room you’re on is higher than the other half. There are a few changes, though.
Inside the coffins are three Stalfos. Firstly, have Link enter the light beam. Draw your sword. Use the Mirror Shield to direct some light at one coffin. Soon, a Stalfos will emerge from it.
If you feel like you take two or even three at once, open the other coffins. If not, go into the pit and make battle with the skeleton. You should remember how to fight this. Just blow up the skeleton (Bombs work decently) and then stun and attack the head repeatedly.
Repeat the process with the other two coffins and Stalfos. When the three monsters are killed, a chest will appear. Climb up the ladder and open the chest to get Treasure Chart #20 . After that, leave.
Whenever you return to the mirror puzzle room, take Medli/control her and throw her/fly her up to the ledge with the door you originally entered through. Pick her up when Link gets up there and go through the door.
When you enter the large cylindrical room, take control of Medli. Have her fly up to the ledge you entered onto earlier. Link will have to take the long way and climb the vines. When Link meets up with Medli, pick her up and get next to the warp jar.
Jump off of the ledge, going towards the boss door, and Medli should fly you there. On the ledge, open some jars to use and/or bottle some fairies. Save and, when ready, go through the door.
When Link enters the boss room, you’ll see quite a few Poes dancing around the room. They all notice him and then turn into their ghostly forms. As they run to the center of the room, a large mask appears and seems to absorb the Poes.
As it does, a blobby form that begins to take on the shape of an extra-large Poe appears. It laughs and summons a lantern. It is none other than the boss of this dungeon, Jalhalla!