When O'Chunks throws Princess Peach, he merely tosses her without doing the spinning and victory pose.
He is not encountered again until Chapter 5. Dimentio sends them all to Dimension D, where they duel. In 5-2, he attacks the same way as before, with the added ability to pick up and throw chunks of the ground at the player. He can also spin back into 2D if stuck in 3D, but still loses to them once again. He asks them to finish him off because he failed the Count, but Dimentio then appears, offering him a chance at redemption. O'Chunks accepts his offer because he "lives for the Count", and then leaves with Dimentio.
O'Chunks is fought again in Chapter 5-4, this time having been brainwashed by a Floro Sprout. He randomly shouts out the names of various vegetables while in this form, which Dimentio nicknamed him O'Cabbage. In this state, his attacks are faster, and he picks up bigger ground chunks. After being defeated, the Floro Sprout on his head shrivels up and falls off his head, erasing his memory of the third fight. He attempts to engage Mario in battle once again, but eventually retreats back to Castle Bleck.
Bowser and O'Chunks trying to lift the ceiling in Castle Bleck. O'Chunks is fought for the fourth and final time in Castle Bleck. Here, he faces off against Bowser in a one-on-one fight as the much bigger Super O'Chunks (the player is unable to play as Princess Peach, Luigi, or Mario in this battle, as Bowser challenges him one-on-one). When he loses, the ceiling begins to collapse. O'Chunks stays and holds it up out of honor for Mario's party, giving them a chance to escape unharmed because " they gained the right to pass". Bowser remains behind to help him instead of leaving though, and after a pointless display of brawn and willingness to sacrifice themselves between the two, the ceiling presumably crushes them both.
However, it is later revealed that he (along with Bowser) survived the cave in because Bowser's weight caused the floor to collapse as well, and they both fell downward unharmed. In addition, O'Chunks also learned from Nastasia about Dimentio's treachery, and also learned from her where Bleck was most likely to be imprisoned. Later, Mimi takes him with her to Dimension D to assist Count Bleck. He and Mimi give the Count and Tippi enough hope to restore the Pure Hearts, thereby helping to defeat Super Dimentio.
After the game has been completed, O'Chunks can be found on the third floor of Flipside by the Heart Pillar searching for Nastasia, hoping to give her some of Saffron's treats