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 a fourth and fifth season before the third season had even started airing.
The Danza: The character Teri is played by Teresa Gallagher. Given Teri is just a supporting character and Gallagher also voices one of the main cast, this was probably a coincidence.
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. The same goes for a flashback with Darwin in "The Extras" to the second season episode "The Sweaters". This is even though "The Kids" established the different voice actor being from a voice change that hadn't happened before the third season.
The first voice of Darwin voiced Gossamer the monster on The Looney Tunes Show and was in the Tyler Perry movie, I Can Do Bad All By Myself (Kwesi Boakye). His replacement voice (Terrell Ransom, Jr.) was on such American shows as Days of Our Lives, The Middle, and Children's Hospital.
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 were recast in season three due to their original voice actors hitting puberty.
In season 1, Sussie was voiced by the creator's girlfriend Aurelie Charbonnier but in season 2 she is replaced by British comedian Fergus Craig. Charbonnier, however, still plays the physical puppet, just with Craig's voice dubbed over.
Almost all voices were recast in the Hungarian version after season 1, save Gumball, Darwin, Nicole, Anais and a few side characters.
Prop Recycling: A lot of the characters are rejected advertising mascots Ben Bocquelet had in his portfolio.
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, Sussie, and (in the second season onward) Carmen is voiced by either Teresa Gallagher or Jessica McDonald.
In an interview (page 127), Ben Bocquelet revealed that the show was originally pitched to [adult swim] (yes, really) and about rejected cartoon characters in a remedial school. Cartoon Network found the idea to be too depressing and Bocquelet changed it to make it a more surreal, whimsical, and kid/family-friendly show.
An "Early Reel" was made for the show as a pilot. 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.
Sarah the Ice Cream's name was originally going to be Dolly◊.
Three episodes were scrapped because they went over budget: season one's "The Mom" and "The Pizza" and season two's "The Rex." However, the premise for "The Mom" may or may not be used as the story for the upcoming season three episode "The Mothers" and "The Pizza" will end up being a season three episode. "The Rex" would have fully introduced Tina's father and have been a parody/homage to Jurassic Park.