Adored by the Network: Cartoon Network gave this a huge buildup: a "sneak peek" six days before the premiere (which also aired on Boomerang and streamed on the website), a countdown bug on-screen the day of the premiere, and at least one rerun a day for the entire week afterward.
The Latin American version of Cartoon Network brings this trope Up to Eleven. They went to such extent to dedicate a whole day to the show. They also use them to announce the new stuff of the month and air reruns three times a day, everyday, and they often air clips of this show during the commercial breaks for no reason at all.
Cartoon Network also put a lot of faith into the show by renewing a second season a week before the premier, though this could have been done as the show spends a long time in production. Cartoon Network later renewed the show for an additional 2 seasons, making the total number of seasons 5, and all before the third season had even started airing.
Dawson Casting: Aside from the Watterson children, kids in the show are played by adults.
Fake American: Most of the adult cast are Brits doing American Accents. Technically averted with Sandra Dickson, who is an American based in the UK.
Flashback with the Other Darrin: A flashback in "The Name" redubs a scene from the first season episode "The Curse" with Gumball's third season voice actor—even though "The Kids" established the different voice actor being from a voice change that hadn't happened yet in the first season.
Interestingly, the Brazilian Nicole and Richard have mentored Rachel Berry; Richard used to be Rachel's high school teacher, whereas Nicole is her current dance instructor. note Nicole didn't date Finn Hudson.
Gumball was voiced by Nicky Jones (aka Chowder) in the pilot.
In the first season Mr. Small, Tobias, Banana Joe, and Alan were all played by Rupert Degas and Ms. Simian was Sandra Searles Dickinson, while in the second season these roles were all taken over by Hugo Harold-Harrison. Tina also changed from Dan Russell to Stefan Ashton Frank, even though Russell continues to play all his other roles (including Richard).
Both Gumball and Darwin have been re-cast for Season 3 due to their voice actors hitting puberty.
In season 1, Sussie was portrayed by the creator's girlfriend Aurelie Charbonnier but in season 2 she is replaced by British comedian Fergus Craig.
Prop Recycling: A lot of the characters are rejected advertising mascots.
Short Run In Peru: Several episodes have aired first in Brazil (Portuguese dub), France, Spain, Central and South America (still in English), and Australia.
Talking to Himself: Most of the dozen plus named students in Elmore Junior High are voiced by a few people, so this happens a lot. In particular, every non-adult female but Anais, Tina, and Sussie is voiced by either Teresa Gallagher or Jessica McDonald.
What Could Have Been: The original pitch for the show was in an "Early Reel". The most noticeable differences are the fact Darwin was animated in CGI and Gumball had a square head, though other characters looked different too. Teri was also a boy, there.
In an interview (page 127), Ben Bocquelet revealed that the show's original premise centered on rejected cartoon characters in a remedial school that helps them be normal. The idea was rejected as Cartoon Network found it "too depressing."