After Flint's sad tale unfolds, we learn of Duster's new quest.
Go to the Castle
Go downstairs and open the boxes, then go outside. Get a Thunder Bomb from behind Wess's house, then go to Cross Road, then go back to Wess's house and get another Thunder Bomb. You can do this as many times as you want.
Go west to the square, then north to Cross Road, then north again to the cemetery, and go north to the castle. Then go south, and go into the gravedigger's hut. Go downstairs, open the gift boxes, then push the bookshelf aside and go through the hole.
Go north to reach Osohe Castle. Go north and check the wall above you, and you will staple the wall to climb up. Go west and go through the door.
Find the Shiny Thing
Go to the left to get an item, then go back to the previous room, stand below the statue, and dash into it to open a hole in the floor. Fall down the hole.
Don't open the gift box here. If you want to go back up, check the middle of the back wall. Otherwise, go through the door on the right.
If you opened the gift box in the previous room and got sick, open the next gift box and use the Fresh Mint to recover from the sickness.
In the next room, go south to unlock the castle door. If you go west and go down the ladder, you find a hot spring where you can heal up.
Go back to central room, and go north from there.
Go through the northwest door. The gift box contains the Battle Memory, which you can use to practice battling past enemies. During practice, the enemies won't attack you, and can't be defeated.
Back in the hallway with the three doors, go through the upper middle door. If you don't have a Rotten Eclair in your inventory, fight Stinky Ghosts until you get one. Then bring it back to this ghost behind the upper middle door of the central room and trade the Rotten Eclair to get the Rope Snake.
Back in the hallway, go west. Go up the stairs to reach a hallway. Go through the first door and open the gift box to get a Chick Bandana. If you need to heal up, you can check the fireplace to go to the hot spring, but be aware that the fireplace is one-way.
Back in the hallway, go east and through the door. You can go through the southeast door to reach the kitchen, where you can get a map of the castle. For a challenge, you can fight the Strawberry Slime.
In the previous room, a ghost will offer you something to eat. If you have a Rotten Eclair, say no. If you don't have a Rotten Eclair, say yes. Check the back wall to go up to the next floor. Then talk to the ghost and give it a Rotten Eclair to get a Beef Jerky. Repeat this to get infinite Beef Jerky.
Go east from the Beef Jerky ghost to get some items, then return to the room with the Beef Jerky ghost. Go to the left, then press A to use the Rope Snake on the candles. Go west to reach the next room, and save the game, then go back and talk to the ghost. Then go into the room and get the Durable Shoes. You can fight the monster if you wish. You can check on the sword or shield to fight the weapons separately, then fight the armor afterward. Or you can approach the armor to fight a tougher version of the enemy.
Then go back to the hallway and exit west. Follow the path to the next floor.
When you reach a hallway with multiple doors, ignore the middle two doors. They are actually enemies. You can fight them for more experience if you prefer. Then go east and go through the rightmost door.
Talk to Mr. Passion to start a boss fight.
Use the Smoke Bomb. Attack with other bombs if you have them.
Check on the couch to heal up. Then go north to get the Noble Spittoon. Go to the previous room and check on the fireplace, then go east and south to leave the castle.
Go east from the castle entrance to find the gravedigger. Talk to him to get the Drawbridge Key.
Go south to the Cross Road, then go south to the square, then go east and enter Wess's house.
After the cutscene, get the Thunder Bomb from behind Wess's house. Then go west to the square. Buy stuff from Thomas's Bazaar if you wish.
Go north to Cross Road. After the cutscene, keep going north to reach the castle. Go inside and you will have to fight the Clayman. Don't be afraid to use the Smoke Bomb and your Thunder Bombs.
After the battle, you can go west if you want to heal up in the hot spring. Otherwise, go north to the hallway with three doors. Go west to the stairs and go to the next floor. Go through the far right door, then climb up the wall staples. Use the rope snake to cross the gap again, and go west, then go up the stairs to the next floor. Go east through the mirror hallway, then go east and go through the far right door. Go north and check on the back wall to start a cutscene.
The path through the next area is straightforward. You will need to use the rope snake to cross some more gaps.
In the broom room, don't let the brooms sweep you, or you will go back to a lower floor.
After the broom room, continue along the path and you will reach a door. Go through the door and go north to start a cutscene. Afterward, you will have to fight a boss.
Use the Smoke Bomb and your Thunder Bombs. Use PK Thunder α. Heal up whenever Oh-So-Snake does a wave attack.
Down the Drain
After the cutscene, go west to reach the square. After a cutscene, the chapter will end.