A number of characters in The Amazing World of Gumball have changed from how they were in the first season, mostly in the case of other students of Elmore Junior High.
- Alan the balloon could act just as antagonistic to Gumball as some the other students, compared to the absurdly Nice Guy he later became. Him bopping Gumball on the head in annoyance in "The Mystery", for example, would be unheard of nowadays. In his first appearance in "The Third", almost every joke about him revolved around his lack of hands rather than his Incorruptible Pure Pureness.
- Hector the giant was your stereotypical Jerk Jock who was stated to play football in one episode then abuse the weaker teammates when they lost. Later episodes portray him as a Gentle Giant who tries to stay as calm as possible, as him being angry has severe consequences to people and property.
- Sussie the chin puppet started off as a relatively normal student who, as she lacked usable arms, had trouble eating and doing homework. More recently she became a full blown Cloud Cuckoo Lander.
- Nicole Watterson was a somewhat level-headed character with anger management issues to start with, but earned herself a need to always win at all costs starting with "The Fridge", effectively leaving Anais as the Only Sane One in the process.
- At times, Darwin could be even dumber than Gumball (particularly in "The Genius"), rather than typically being the brains of the two, if a bit naïve.
- Gumball Watterson himself was initially a Cheerful Child to an almost absurdly, but later became more of a snarky and cynical Jerk with a Heart of Gold (though some of the old personality remained in regards to his obliviousness to how much Mr. Robinson hated him). Also, in earlier seasons, Gumball and Darwin were Super Gullible, as seen in "The Car" and "The Spoon". In later seasons, while Gumball couldn't exactly be called smart, he is increasingly often the Only Sane Man with The Ditz role belonging wholly to his father Richard.
- Principal Brown in Seasons 1 and 2 came off as a Dean Bitterman or extremely Apathetic Teacher, as shown in "The Lesson" where he treats the kids in detention like hardened criminals and in "The Genius" where he sees nothing wrong with kidnapping children just for being smart. Later he became more just a well-meaning but incompetent goofball, and while he still often gets mad at Gumball and Darwin, he generally has a good reason for it.
- Jamie was always stated to be a bully, but for the first two seasons this was mostly an Informed Attribute, and the worst thing we ever actually saw her do was cut in line. The same episode showed that she was clearly not well-liked, but her classmates didn't seem afraid of her at all, and Darwin not objecting when she cuts in line was just seen as a sign of his timidity. Beginning with the revelation in "The Coach" that she's eaten bits of her classmates on several occasions, she's portrayed as a complete psychopath whom everyone in the school is so terrified of that they basically just let her do whatever she wants.
- In Tobias' first appearance in "The Third", it seems people genuinely think he's as great as he claims even though he's obviously not. In later seasons, he's one of the least popular kids in the school.
- The earlier seasons showed Mrs. Robinson as more or less a gender-flipped (if slightly naggy) version of her husband Mr. Robinson. Then the Season 4 episode "The Wicked" established her as a maniac who makes people miserable For the Evulz.
- Ocho was implied to have anger problems in an early description, but he initially spoke just in arcade sounds and his anger was only seen by his always angry face, other than that, being just a Flat Character. In the second season, his anger issues are explored, and he is shown to shoot beams who can cause explosions and destroy people and things. In another episode in the fifth seasons, a crazy side of him is shown too; he kidnaps someone as a prank, and forces Gumball to be his best friend, making a ritual.
- Hot Dog Guy was initially just an extra in cafeteria scenes. Later in "The Hug", Gumball tries to talk to him to show Darwin he is not unpredictable, and begins bumping accidentally to him several times. This happens again in "The Awkwardness" and in a small scene from "The List". "The Cringe" reveals that their accidental encounters did not begin in "The Hug"; that has been happening since they were little kids.
- In Season 1, Mr. Small being a hippie was only implied through his fashion sense. His primary trait was instead his violent mood swings (to the point where some have theorized him as having bipolar disorder), and occasionally he could be just as much of a Jerkass as Miss Simian or Principal Brown. Come Season 2, his hippie nature is much more pronounced, his mood swings are much rarer, he gets his now-signature interests in alternative medicine, environmentalism, and conspiracy theories, and he shows a genuine love of teaching and inspiring his students.
