"The Mustache" is the twenty-sixth episode of Season 1 of The Amazing World of Gumball.
When Gumball, Darwin & Anais accidently eat supplements meant for Richard, they become "men."
The episode opens with Richard struggling to open a box of Daisy Flakes, when he gives up and throws the box away, claiming it to be "useless." Gumball and Darwin trudge into the dining room, complaining that they don't feel like going to school today. Richard tells them that they must go to school anyways because they're still kids and they have no control over their lives. Richard absentmindedly hands them what he thinks is their cereal while Gumball and Darwin dreamily describe what they'd do if they were men.
Later that morning, Gumball and Darwin are riding the bus to school when they happen to see a Shooting Star standing near a bus stop. They wish upon the star to make them into men, which disappointingly doesn't turn them into men, so they throw a can at him.
At school, Miss Simian is teaching her students about the effects of puberty. Gumball and Darwin are passing notes, Gumball's depicts him calling his receptionist at work and Darwin's depicts him voting. Miss Simian spots the two passing the notes and claims that they're at least on topic. The lesson carries on, and Miss Simian begins the topic of acne, during which a large pimple sprouts on Darwin's head. Gumball attempts to hide it by putting a small bowling hat on it, but more appear on Darwin. Darwin asks why Gumball doesn't have any which Gumball replies, "Just lucky I guess", but when he turns his head around, it can be seen that he also has a lot of acne. Both of them start to scream and freak out.
In a panic, Gumball and Darwin run into the girls' bathroom on accident. They manage to pop all the pimples, but Darwin starts growing facial hair soon after. After Gumball attempts to remove it (using bubblegum instead of wax), they both regrow the hair and a uni brow. They scream at each other in horror, to which Penny reminds them that they are in the girls' bathroom. Gumball and Darwin remove all their hair with gum and return to class.
During School Gym, Miss Simian announces that they're going to play dodgeball, which Gumball can't stand. Tina comes over to Gumball and remarks that's he's going to get pummeled, which he does unfortunately. After almost being hit with a bowling ball, Gumball decides he has had enough, as his arms begin to grow to massive proportions, his body becomes ripped, and the mustaches grow back. He throws a dodgeball with terrifying strength, which hits Tina and sends her crashing through the wall. Gumball looks back at Darwin, who had just gone through exactly the same changes. As they both scream in terror, their voices deepen drastically.
Gumball and Darwin lock themselves in the boys' bathroom, claiming that they've been turned into monsters, and have to be coaxed out by Miss Simian. She tells them that it is just a part of life and that they have to get back to class, but Gumball realizes that they don't need to listen to her anymore, because they're men.
Gumball and Darwin test drive a car, pay more for the movies, and even consider having their own kids. Although they soon realize that they can't since they don't have jobs. They go to an office, where they're interviewed by the Cupcake Woman. Since neither of them have any special talents, she refuses to consider them for a job, but they both persist, which irritates her so much that she gives up her job to Gumball and Darwin.
Gumball and Darwin aren't sure what they're supposed to be doing, but they do know that they can fire and hire people. They both go around the office, firing and hiring random people at their own will, even firing each other by accident. Gumball and Darwin stay at their new home, a run down apartment, and begin to have regrets about them wanting to become men.
A sudden knock at the door wakes them up, as a large, looming figure stands at the door. Gumball and Darwin believe it is the landlord, but surprisingly, the looming figure is Anais, sporting a mustache and a large stature. She explains to Gumball and Darwin that the entire thing was a large misunderstanding and urges them both to come home with her.
At home, Richard is worrying about his physique while Nicole is attempting to comfort him. The kids come in, and Anais reveals that in the morning, Richard accidentally switched the cereal with protein supplements, causing the children to all suddenly grow.
Nicole asks Richard why he bought protein supplements, and he explains that whenever he checks his e-mail, the advertisements intimidate him into buying whatever they're selling. Nicole discovers that the supplements wear off in about a week, as the episode ends with the still gigantic kids having fun at the park, much to the confusion of the other citizens at the playground.
- It is impossible for fish to grow hair, because they have no hair follicles.
- According to Gumball, Nicole waxes often, which is strange because, like Gumball, she's covered in fur.
- Oddly enough, Richard's supplements affected Anais the most, despite her being a female child. This mirrors the effects of testosterone supplements on females, where they develop male-like characteristics.
- In the apartment which Gumball and Darwin shared, there is a pair of UK plug sockets on the wall above the couch.
- This is the second time that we have seen a family laptop destroyed. The first time was in "The Responsible." It happens again in "The Phone."
- This is the second time we see Darwin's butt. (Third time if one counts the trailer)
- This is the second time Darwin grows hair; the first time was in "The Refund."
- In "The Dress," Darwin is shown to have decent artistic skills but in this episode, his drawings mimic that of a four year old. This would be mentioned again in "The Procrastinators."
- This episode is an obvious parody of the 1988 film Big, where young Joshua Baskin wishes to be big, and his wish is granted. But after a few weeks, Josh discovers the joy and wonder of being a kid.
- The song "Because We're Men" is a parody of the song "Now That We're Men" from The SpongeBob SquarePants Movie.
- Gumball and Darwin are seen as completely hairless at one point. This is unusual in Darwin's case because he doesn't have fur. Moments later, their skin returns to normal.
- Gumball's whiskers were not visible while he was getting pelted by dodgeballs.
- When Gumball and Darwin were being pelted by dodgeballs, the second time Darwin screamed "My ankle!" his mouth did not move.
- If you look closely when the kids were in class, Leslie's pen is in mid-air.
- Before Gumball and Darwin panicked and hid in the girl's bathroom, Penny can be seen in the classroom. However when Gumball and Darwin were in the bathroom, she is already at the bathroom stall with no given explanation on how she got there before they did.