The Authority/The Virus - S2-E10
Revealing mistake: In "The Authority," when the Wattersons return to normal and start screaming "The brake!", Darwin's animation repeats itself in the same frame. Thanks to the slow motion the scene is going in, this error is easy to spot.
The Mothers - S3-E17
Plot hole: When the "refrigerator" falls on Tobias's mom, the boys are watching from a side view. It is later revealed that the fridge was just a cardboard cutout. The boys were watching from the side, so how did they not notice it?
Nicole Watterson: Well maybe it all comes back to the stupid name you gave me!
Gumball Watterson: Um, what's wrong with Nicole?
Nicole Watterson: Nicole is my middle name, my first name is DOCTOR!
Trivia: The voice of Gumball in Japan is voiced by Junko Takeuchi, who is also the voice of Naruto Uzumaki.