Larry mentions a Running Gag that happened in Season 1. It was when Larry tried to marry Karen but the Wattersons interrupted it.
There are lots of flashbacks from previous episodes that are altered by Zach.
Mollyreturns to the show, but she was absent for season 2 (save for cameos on pictures from "The Words" and "The Sidekick"). Not only does she return, but her return is the entire plot for the episode.
Rob appears in the void of mistakes, which was more than likely because he was forgettable in "The Pony".
When Darwin sees Banana Barbara's painting of him and Carrie kissing each other (from "Halloween"), he seems embarrassed about it.
Anais encounters a painting of her and her brothers sneaking into Tina Rex's bedroom to get Daisy the Donkey back (from "The Quest").
Rob becomes the Big Bad. And it is because he was ignored by Gumball and Darwin during the events of "The Void".
Masami's Rich Bitch personality is briefly referenced in this episode. She was revealed to be a Rich Bitch in "The Words" and was the antagonist in "The Storm".
Rob, the person who swore to get revenge on Gumball and Darwin for ignoring him, reappears. And he officially becomes their nemesis.
Richard's father, Frankie (who was mentioned in "The Man" that he went away to buy milk years ago) not only returns, but the fact that he "went away to buy milk" is also referenced.
Gumball succeeds in transforming into a Super Saiyan. He tries to transform into a Super Saiyan before, in "The Others".
Anais abhors Billy, which is because the latter admitted to hating Daisy the Donkey in "The Egg".
Rob appears on an Elmore Stream video, saying "Revenge". This is obviously because of the incident that happened during the events of "The Void".
Rob says "love has no name". In "The Pony", Gumball and Darwin completely forgot about his name. It's not just a coincidence
The Evil Turtle has another major role. And she is now revealed to be pregnant.
Rob tells Gumball that he is Dr. Wrecker to him. Dr. Wrecker is Rob's alias as of "The Nemesis".
Gumball says he thought he would have 15 minutes of fame. He said that before in The Oracle.
Rob says he will destroy everyone Gumball loves. He said this in "The Nobody".
Rob accidentally hits the rewind button, causing him to go back in time... to the events of "The Void" and "The Nobody"!
Molly is said to be boring in "The Void". She really is boring in "The Stories"...
Gumball said in "The Apology" that it would be cool to see Tina Rex and Bobert fight against each other. Guess what? This happens for real in this episode!
Carrie and Darwin's crushes on each other were referenced in "The Scam" and "Halloween". In this episode it is not only referenced again but now they become an Official Couple.
The ability to summon ghosts by saying their names five times is reused (Gumball summoned Carrie). You can just say their names thrice to summon ghosts, though.
Carrie's ability to possess people and control them happens again. It happened before in "The Ghost" and "The Mirror.
At the same scene, Karen calls Larry Laurence. How big of a Call-Back is this?
Penny is out of her shell ever since "The Shell" (excluding some animation errors where she is on the school bus, still in her shell). This episode even revolves around her shell being taken off!
Banana Barbara's ability to paint the future from "The Oracle" has a major role in this episode.
Excluding the painting of the Wattersons in the void, Banana Barbara's paintings contain scenes of previous episodes.note To be more specific, scenes from "The Others", "The Shell", "The Signal", "The Nobody", "The Job", "The Signature", "The Boredom", "The Bus", "The Void", "The Butterfly", "The Quest", "The Oracle", "The Money", "The Rerun", "The Allergy", "The Finale", "The Oracle", "The Name", "The Society", "The DVD", "The Night", "The Rerun", "The Void"
The guy in static from "The Future" appears in this episode, and is Superintendent Evil.
Banana Barbara's painting of Rob falling into the void from "The Future" also happens in this episode.
Gumball calls Miss Simian two-faced. Nicole called Miss Simian a two-faced baboon in "The Ape" though.