Tropes
- A Boy and His X: A boy and his fish, the boy being Gumball and the fish being Darwin.
- A Day in the Limelight: The second half is focused on how Darwin returns to Elmore and how he becomes a fish with legs and lungs.
- Accidental Ventriloquism: Richard hears the shop keeper talking from inside the van and assumes the van itself is talking.
- Big Damn Reunion: When reunited again, Gumball and Darwin run into each other's arms in slow motion and a heart explodes behind them.
- Black Comedy Burst:
- Richard and Nicole think they have the same plan to deal with Gumball's hyperactivity, but while Nicole wanted to get him a pet, Richard starts to say they should go back in time and prevent Gumball from being conceived. Richard suddenly cuts himself off before he can complete the sentence and nervously claims his idea was also to get a pet.
- The many goldfish before Darwin die in sequence, punctuated by Richard singing "Swing Low, Sweet Chariot" in a falsetto voice and flushing the toilet — until Larry the clerk tells Richard he can't sell him anymore because the last two escaped.
- Darwin startles Sussie's parents into dropping her, which turns her from a brainy, talkative child with dreams of being a lawyer to a barely-coherent idiot.
- Bowdlerization: On Cartoon Network MENA (Middle East/North Africa), the opening scene of Gumball throwing oranges out the window and Nicole yelling, "Gumball, stop using my bikini to catapult oranges at your dad!" had Nicole's bikini line changed to, "Gumball! Those are oranges, not soccer balls!"
- Call-Forward:
- Richard buys Darwin from the same shady red van he would later buy the killer turtle in "The Puppy".
- Nicole gets the idea for her job at the Rainbow Factory when she sees it under construction.
- We find out where Darwin got his shoes. Gumball gives him his own.
- The dog catcher who tranquilizes Darwin is the cockroach pest control worker called to take down Penny when she freaked out over her new form on "The Shell".
- Childhood Brain Damage: Sussie is shown as a verbose and intelligent infant, until Darwin bumps into her parents and they accidentally drop her. When they pick her up, she's making the bizarre noises she typically makes in the present.
- Continuity Nod: Richard is confused by Gumball gesturing to his chest and thinks he's referring to his stomach. Nicole has to remind him that not everyone's stomach fills their whole chest, a detail established for Richard in Freeze-Frame Bonus in The Traitor.
- Determinator: Darwin stops at nothing to get back to Gumball and Gumball has faith that Darwin will come back (even when it seemed like it would never happen).
- Death Montage: A goldfish dies, Richard flushes the corpse in the toilet while singing "Swing Low, Sweet Chariot", and buys a new one without Gumball seeing it. This repeats up until the last two goldfish literally escape from his sight.
- Did Not Think This Through: Gumball did not realize his command for Darwin made him look dead, and thus in danger of being flushed down the toilet.
- Do You Want to Haggle?: The shop owner first claims Darwin isn't for sale, but admits that was just a starting line for negotiating a price. Richard talks to the owner to lower the price from $100 to $10. When the owner acquiesces, Richard raises the price to $50. When the owner expresses confusion, Richard decides to pay him the $100 originally asked for.
- Dumbass Has a Point: Richard points out the whole "don't feed after midnight" concept doesn't make sense given it's always after midnight.
- Flashback To Catch Phrase: We see when Darwin started calling his parents "Mr. Dad" and "Mrs. Mom".Darwin: I know you didn't flush me on purpose Mr. Watterson.
Richard: Please son, call me dad.
Darwin: OK, Mr. Dad. - Formula-Breaking Episode: The show's first two-part episode and a Whole Episode Flashback showing what Gumball was like when he was four, what Nicole and Richard were like when they were young parents, and how Darwin became Gumball's brother.
- Four Legs Good, Two Legs Better: When Darwin first gets legs, he quickly concludes that it's easiest to move around on all four limbs. Once in the dog catcher's van, Darwin standing up lets him reach the keys to the cages and he walks upright from then on.
- From the Mouths of Babes: Nicole tries to explain to Gumball that the Darwin they recently brought wasn't his first fish, but backs off and claims the others fell asleep, were put in a "super fun water slide that goes round and round", and are hanging out in an "magic place" together. Gumball, at 4 years old, not only figures out what actually happened to the other fish, but takes it in stride.Gumball: Are you saying you replaced the fish because they croaked and then Dad flushed them down the toilet?
- Fun with Alphabet Soup: Gumball picks a name for Darwin by mixing his alphabet soup. However, the soup actually reads "JPXFRD", Gumball just can't read yet.
- Fun with Flushing:Darwin is accidentally flushed down the toilet.
- Furry Reminder: Some of Gumball and Darwin's future classmates have appearances reflecting their non-human nature:
- In the short scene of Gumball and Richard swimming in the lake, Banana Joe is still green because he hasn't ripened yet.
- Leslie's hasn't bloomed yet, so his petals cover his face and blind him, causing him to kill one of the Darwins by kicking its bowl.
- Teri's face is drawn like a child's scribbles and her body is crudely cut out, also as if done by a child.
- How Is That Even Possible?: Gumball somehow gets sand and snow into the house (it's not winter and the Wattersons don't live near a beach), and also leaves footprints on the ceiling. Nicole questions how he did it, but decides to not press the issue after seeing the footprints.
- I Will Find You: Darwin will stop at nothing to get back to Gumball, and Gumball refuses to give up on him doing so.
- The Jinx: The Wattersons have such bad luck with goldfish that the last two fish jump out of the tank when they see Richard coming.
- Multi-Part Episode: Consists of two quarter-hour episodes. This is the first one for the series, as the staff held off in earlier seasons out of fear that the episodes would air out of order.
- Musicalis Interruptus: Darwin's song is interrupted when an eagle suddenly snatches him up. When she tries to feed him to her chick, Darwin slaps the chick in the face and continues crawling on while singing.
- Narrative Shapeshifting: Darwin is able to change shape and even color to imitate others for the sake of communicating. He makes himself look like Richard when asked to look dumb, and makes himself to look like Gumball when asking around for him.
- No Cartoon Fish: While Darwin looked just as stylized before growing legs as after, the earlier Darwins were nearly photorealistic and unexpressive, though the last two were apparently intelligent enough to jump out the tank in Larry's pet store when Richard came to buy yet another goldfish. The fish Darwin meets at the ocean are somewhere in between, being realistically-shaped but simple while having a largely human range of expressions.
- Not So Above It All:
- Gumball and Richard end up killing one of the goldfish each. Nicole ends up killing two of them.
- Richard tries to condole Gumball over Darwin's absence, and Nicole cuts him off because he thought he was going to say "There's plenty more fish in the sea". When Richard explains he was going to say something else ("There's plenty more love in a heart for a new friend."), Nicole says it herself just to correct him and regrets it immediately, while Richard looks on disapprovingly.
- Origins Episode: As indicated by the title, this episode shows how Darwin became a member of the Watterson family.
- Previously on…: Parodied, as most of the clips used are from episodes that came before this one and have nothing to do with the actual episode.
- Puff of Logic: Darwin starts running around in panic when he gains legs, but then realizes he doesn't know how to run and flops to the ground.
- Replacement Goldfish: Every Darwin was meant to replace the last, but the Darwin who stayed around quickly becomes a treasured member of the family.
- Series Continuity Error:
- In this episode, there were at least six goldfish before Darwin was chosen as Gumball's pet and all of them were flushed down the toilet. In "The Party" Darwin's full name ("Darwin Radlin Caspian Ahab Poseidon Nicodemus Watterson III") implied he was the third goldfish and in "The Game" Nicole finds the skeleton of the first Darwin under Gumball's bed.
- In "The Bet", Gumball states Darwin took five years to learn facial expressions, but he has no problem with them here.
- In "The Hero", there's a photo of Richard giving Darwin to Gumball on Christmas. This episode clearly is not set on Christmas.
- Shout-Out: The two warnings given by the Awesome Store owner to Richard ("don't get the fish wet" and "don't feed it after midnight") are taken from Gremlins (1984).
- Sleep Cute: The episode ends with Gumball and Darwin reunited and falling asleep together in the back of the family car.
- Smash Cut: Richard realizes the third replacement goldfish he bought was the wrong color, so he tries to paint the fish orange. Just as the brush is about to reach the water, there's an abrupt cut to a shot of orange water being flushed down the toilet and Richard singing "Swing Low, Sweet Chariot".
- "Somewhere" Song: Darwin sings "I'm On My Way" once he gets lungs, about how nothing will stop him from getting home to Gumball, getting slower and more desperate as Darwin begins to tire and dry out.
- Surprisingly Realistic Outcome: Richard tries to paint a black fish orange to keep Gumball from finding out that he has a replacement fish. When most cartoons would have the fish painted without any consequences, they immediately die because the paint dissolved into their water.
- The Power of Love: Darwin's connection with Gumball is what made him able to survive on dry land and grow legs.
- The Little Shop That Wasn't There Yesterday: Darwin was bought from a mysterious van store, the same one from "The Puppy", with the owner even saying Darwin was more then he appears.
- Travel Montage: Spoofed with Darwin actually walking over a map someone dropped on the forest and mistaking it for the actual destination.
- Whole Episode Flashback: The entire episode takes place about eight years ago, with no present-day framing device.
- Whole-Plot Reference: The idea of a child losing their beloved fish, only for the fish to develop into a human-like being and go searching for their owner, seems to have taken inspiration from Ponyo on the Cliff by the Sea which has the exact same premise.
- Your Size May Vary: We are explicitly shown Darwin growing lungs and legs, but his growth to human size seems to happen inexplicably between growing legs and making it to Elmore.
