Once you climb up into the next room, you'll have to do some carefully timed jumps, making use of the extending spikes, to progress upwards. Use the floating platform to jump onto the rope on the upper left and climb up it. The next room is a small one, but it has two big bats inside it you'll have to kill. Once they're dead, climb up the top on the right to enter a difficult room. There's a punaguchi in it, but it's on a small floating platform, and the only way you can get to it is by using the extending spike. Try getting in, getting one or two hits, the getting out and repeating this until the punaguchi is dead, then use the floating platform it was on to get to the ledges on the right. Then climb up the rope.

Climb up this rope and you'll arrive in a room you've already been in. If you go all the way up the rope, you'll be in a loop, doing the last few rooms you were in. Instead, head down the rope, and then start doing the rooms in reverse order. Once you've cleared the room with the two big bats in it, head down the rope on the left...

...and you'll arrive in a room you haven't been in before. This is another small room with a floating platform in it, jump onto it and carefully kill the punaguchis before heading through the door. The next room is a long corridor, where lots of mud men will keep appearing. Fight them off and keep going right until the scenery changes, then hit the single candle you see. This contains a crystal, collect it to make the Bone Dragon King appear. This creature bursts through the ceiling and floor of the corridor. What's different with this boss battle is that the screen is constantly scrolling to the right.

You can tell which hole the boss will emerge from next as it will shake about a second before it appears. Due to its length, the boss can appear out of more than one hole at the same time, so try and keep to the right of the screen to avoid being crushed. Touching the boss will result in a large amount of damage, but this is the only way it can hurt you, it doesn't have any other attacks. The only place you can hit the boss is on its head, so be ready to try and get a couple of attacks on it whenever it bursts out of a hole. Once defeated, the Bone Dragon King will explode into nothing.