Chapter 2: Thief Adventure is the second chapter of Mother 3, proceeded by Chapter 1: Night of the Funeral and succeeded by Chapter 3: The Suspicious Peddler. This chapter features Duster as the main character and introduces Kumatora as a playable party member later in the chapter. It takes place almost entirely in Osohe Castle.
Chapter 2 begins with Wess telling Duster that the time has come for him to put his thief training to the test. Duster is told to sneak into the Osohe Castle and retrieve a very important item, his only clue being that it is very shiny. After Wess finishes telling Duster what to do, Duster takes his Thief's Tools and heads to the castle.
Along the way, Duster encounters Butch just north of town. He tells Duster a secret: he sold his pigs to someone (who later turns out to be Fassad) for a gracious amount of money; however, the people of Tazmily Village do not know what money is at this time. Butch hides his money in the well at the center of the village and leaves. Duster then proceeds to the castle.
As Duster steps into the cemetery, a cutscene shows a flying object belonging to the Pigmask Army dropping something near the castle. Duster is then be attacked by four zombies before being able to head into the castle.When he arrives, he is unable to proceed because the drawbridge is up. However, Nippolyte has a secret passage in his shack that leads into the castle that Duster takes.
After fighting his way through the underground path, Duster ends up inside the castle walls. Since the portcullis is blocking the easy way in, he uses his Wall Staples to climb his way up the castle wall for another entrance. Duster heads into the castle. It is here that the Battle Memory is obtained.
Initially, every path Duster can take is a dead end, so he trades a Rotten Eclair to a ghost to get the Rope Snake. In the castle, there are various enemies, including ghosts, spiders, and suits of armor. With a Rope Snake, he can get across a gap which was previously impossible, opening up a new path. Just beyond this gap is a door leading to the optional enemy Ghost Knight.
Eventually, Duster notices a girl appear to drop from the ceiling. Upon landing, she promptly dashes through the nearby door and drops her pendant. Duster takes this pendant and proceeds, eventually coming upon Mr. Passion. Duster upsets Mr. Passion by refusing to listen to the music, and the two will then begin battle.
After Mr. Passion is defeated, Duster advances into the next room and takes the Noble Spittoon, which is what he believes is the item that Wess was looking for. Duster leaves the castle, and is given a drawbridge key so he can return to the castle easier. Afterwards, he returns to Wess to report his success.
Duster gives the spittoon to Wess, who is in awe at its shininess, but ultimately smashes it and scolds Duster; this is not actually the item that Wess needed. Wess decides that the only way he will get what he needs is if he goes with Duster. They head back to the castle, and find that the Pigmask Army is invading it. Entering the castle, they are confronted by two Pigmasks and a Clayman.
Defeating the Clayman will scare the two Pigmasks off, but there are many more unfriendly Pigmasks in the castle. Duster leads Wess back to the room with the Noble Spittoon, which again looks like a dead end. Wess observes the markings on the wall, scolding Duster for not knowing what the marks were for. It turns out these markings are instructions for a dance that will open up a new path. Wess asks Duster to look away while he performs the dance, but Duster secretly watches.
The two continue on their path and eventually find the girl that Duster saw earlier, except this time her leg is trapped. She recognizes Wess, and they eventually free her and give her back the pendant. She reveals that her name as Kumatora and joins their party, aiding them with her PSI abilities. They continue through the castle, and eventually find the “certain important item” that Wess was talking about earlier, the Egg of Light.
After talking about it for a few minutes, they are interrupted by a banging on the door; the Pigmasks are trying to get in. Kumatora's reaction is to promptly grab the Egg of Light, but this opens up a trapdoor and sends them down into a pool with a boss, the Oh-So-Snake.
Once the snake is defeated, a drain opens (later revealed to be pulled by Salsa), and all three of them are sucked out. Wess and Kumatora end up on a shore in Tazmily Village, but Duster and the Egg of Light are nowhere to be found. Shortly later, Lighter and Fuel find the two and bring them back to health at their house.
Once they wake up, they realize Duster is not with them, and head to the town square to look for him. He isn't there either, but everyone else is, including Butch, who accuses Duster of stealing the money from the well (although in reality, it was Fassad). Kumatora and Wess attempt to defend him, which is not working too well until Flint comes in and calms the villagers down. Chapter 2 then comes to a close, and Chapter 3 begins.