Chugga having trouble finding the last ten purple coins in the first purple coin mission, and then he actually falls through a planet, getting stuck there.
Episode 25:
Chugga's reaction when he realized that the next galaxy was Sea Slide Galaxy.
Then there's Chugga's reaction when he fails to get the star in the Cosmic Luigi race after he does so well.
Before starting the Engine Dome's boss level, Chugga lists all of the times an Engine Dome level was a rip-off of another level, and when he checks the mission title, it turns out to be a recycled boss.
Chugga: Even the boss level's a rip-off.
Whilst taking the Boo Path, him having difficulty with the Rainbow Star section.
"Let's not fail this time please. Please. Please. Please. Please. Please. Make it-make it-make it-make it-make-it-make it-make it... crap!"