In an episode of Aaahh!!! Real Monsters, Oblina pretends to be a human in order for the school to gather information on them. Unfortunately, she has a bad reaction to some cotton candy and begins to think she really is human.
Taken to ludicrous extremes by Roger in American Dad!, who has a tendency to create personas to go with his various disguises and then almost immediately lose himself in them.
In the episode "The One That Got Away", Roger discovers extra bills on his credit card and immediately sets out to destroy the thief's life. It's halfway through the episode, right around when he's about to set the thief's apartment on fire, when Roger discovers the "thief", Sidney Huffman, is himself under another persona he created specifically to seduce a shop girl so he could steal a pair of gloves he likes. The stress of actually caring about someone else caused Roger's mind to split into two - the persona he created, and himself.
Sidney isn't even the only persona of Roger's with a life of its own: others include Jeannie Gold, a wedding planner with two adult sons, and Max Jets, a man who's been in prison for the last six years and is about to be released, forcing Roger to break in to prison so Max can be released.
Klaus takes advantage of this tendency in "Dr. Klaustus". When Roger, under the "Sgt. Pepper" persona, refuses to return to America, feeling he's no longer fit for society, Klaus waits until he falls asleep and then redresses him as "Dr. Penguin", the family therapist. When Roger wakes up the next morning and sees himself in the mirror, his compulsion to fully absorb himself into a role is so strong that he doesn't even question that he spent the last several weeks as a soldier in Iraq.
"Jenny Fromdabloc" established that Roger can move really fast, which allows him to fake the eponymous persona's death and tie up the episode's plot. From that point, the writers have taken that as free reign to give Roger the ability to teleport whenever he's not on-screen and instantly change personas, allowing for a network of Roger personalities so vast that, among other things, Roger apparently became as good an actor as he is by taking acting lessons from himself. This has been lampshaded several times as well, such as in multiple occasions where someone is pointed to an expert on some subject only to be dismayed to learn it's just Roger in another persona; this eventually reached the point that when a season 12 episode revolved around a collection of a famous artist's works being hosted in town, the whole family is surprised to learn that it's not Roger - Roger included.
In the third season of Amphibia, Grime and Sasha escape Andrias and hide out in Wartwood, telling the citizens that Anne and the Plantars are off on a "secret mission" and sent them to protect the town in their absence. Since they leave out the part where they betrayed Anne again, and the last the villagers saw them, they were on decent terms with Anne, this is believable enough and allows them to avoid too many questions. However, Sasha, finally realizing that Being Evil Sucks, is overwhelmed by guilt for her past actions and hates the lying. When Andrias sends his forces after them, Grime wants to skip town and leave Wartwood to perish, but Sasha refuses, throwing herself in between a Killer Robot and the villagers. In the end, she confesses everything to the villagers, but resolves to stay and become their protector for real, both to atone for the damage she caused and because she's realized Good Feels Good. Grime also sticks around, less because of a change of heart and more because he's loyal to Sasha and will stay with her no matter what she decides.
Subverted in one season finale of Aqua Teen Hunger Force, where the Teens were revealed to be secret agents of some sort and Carl was a secret agent assigned to spy on them. At the end of the episode, he mixes up strip club and liquor store, implying that the real Carl does not share the... interests of the Carl we've come to know and love. Of course, given what show we're talking about, this didn't carry over into the next season.
In As Told by Ginger, Mipsy uses her cousin, Thea, to try to influence Ginger to stay at a private boarding school. Thea spends a semester with Ginger, and during the process, warms up to her and admits she felt bad about the deception, but only did so because she really needed the money to fund her shopping addiction. It's not hard to interpret that she legitimately wanted Ginger to stay because she liked her.
In hindsight, Azula of Avatar: The Last Airbender is this. With no attachment to her mother and nobody to reel in/curb the more disturbing aspects of her, she drunk down the propaganda of the Fire Nation and emulated her father. Believing herself to be Ursa's failure, she took up the mantle of the monster as she believed that's what Ursa saw her as. Hence, this is what created "The sociopath" and "The Monster" personae she adopted and used. However, limitations to these philosophies combined with the realization yet continued denial of this (from Mai and Ty Lee's betrayal) bites her hard comes series' end. Starting from the tie-in comic "The Search", it's clear that the term "Monster" starts to hurt a lot harder than normal.
Done dramatically in the Batman: The Animated Series episode "His Silicon Soul". An android duplicate of Batman created by the mad computer HARDAC is trying to complete its mission, breaking into the Bat-Cave to hijack control of the computers and resume HARDAC's mission, replacing all of humanity with robotic duplicates. But it seems that HARDAC duplicated Batman's personality only too well, and it starts to develop the true Batman's sense of morals, struggling between right and wrong and whether to do as its programming commands or reject what it knows is evil. Eventually, after a fight with the real Batman where the android thinks that it has killed him, it is overcome with grief over what it has done, and destroys the computer, destroying HARDAC's program and itself in the process, ending HARDAC's threat forever. In the final scene, Alfred and Batman — who survived, naturally — inspect the androids remains, and Batman ponders if it might have had a soul. "A soul of silicon," muses the Dark Knight, "but a soul nonetheless..."
The assassin droid Zeta in Batman Beyond replaced an accountant, as he was investigating money laundering by a terrorist organization. Once he completed the mission he ended up running into the guy he was impersonating. Per protocol, he should have eliminated the man on the spot. The aforementioned time spent with the man's family affected him to the point that he could not bring himself to deprive him of that experience, and so went rogue instead (leading into his Spin-Off series, The Zeta Project).
Codename: Kids Next Door: Numbuh 274, aka Chad Dickson. While he remains loyal to Kids Next Door as a Fake Defector, his hatred of Numbuh 1 becomes real due to a perceived slight that Nigel is completely unaware of until the Grand Finale, and he spends his last appearance in the penultimate episode trying to kill him.
Hopelessly averted in the Danger Mouse episode "There's a Penfold In My Suit". Penfold thinks he can be brave and heroic by putting on one of DM's white jumpsuits. Epic fail.
Danny Phantom: Danny's mysterious 12-year old cousin Danielle, or Dani for short, turned out to be his Opposite-Sex Clone created by his Arch-Enemy, Vlad Plasmius, in a plot to use his DNA to create a clone for a son. Danielle was likely ordered to pretend to be family to make Danny trust her. However, Danny grew fond of her and didn't want to harm her, along with shielding her from Vlad. Even with her true identity revealed, they still see each other as family and care for each other.
Discussed in the Daria TV movie "Is It Fall Yet?", when Daria's mom forces her to work as a counselor at a day-camp for children.
Daria: And I judge myself unfit for human contact. Helen: That's exactly what you will be if you don't start engaging with the rest of us! You keep hiding your real face behind that antisocial mask and one day the mask will be your face. I'm not letting that happen. You're working at that camp! (leaves)
Drawn Together: Parodied in "A Very Special Drawn Together Afterschool Special". Xandir is afraid to tell his parents that he's gay, so he and his housemates do some role-playing. It goes so far that the housemates start to believe they're the people they're pretending to be.
"Can someone explain to me why we're doing this when Xandir's not around?"
In Ed, Edd n Eddy, Eddy decides to dress up as a foreign exchange student named 'Carl', to find out who wrote graffiti about him. When he introduces himself to the rest of the kids, he finds out that they all prefer him, instead of Eddy. Double D (the one who wrote "Eddy is a no neck chump" in the first place) tells the surprised 'Carl' that it's respect, and that he hasn't done anything to provoke a negative opinion, like scamming for pocket change.
In another episode, Edd builds a monster suit for Ed, only for Ed to start believing he actually is a monster and proceeds to go on a rampage through the neighborhood.
Peter pretended to attend Meg's high school to discourage the students from licking toads, but he eventually started thinking he was a real teenager. "Eventually" here meaning "after about one day" ... this is Peter we're talking about.
"Brian Writes a Bestseller": Though his original intention was to write trash out of sheer frustration, the work began to garner fame and appreciation from the looked-down-at people and he started to really believe he was a genius, and he had created a life-changing masterpiece.
An episode of Fillmore! has Ingrid going undercover in a close-knit mafia-esque Girl Scout Troop. She genuinely befriends the group, making it especially hard to go through the sting. As an added bonus, their leader was the Safety Patrol's previous undercover agent gone rogue who was much more loved and popular than Ingrid, which made them believe Ingrid could be more susceptible to this op.
Green Eggs and Ham (2019): Sam was the true villain the entire time, wanting to turn Mr. Jenkins in as he's actually an animal-smuggling scam artist. But his time on the run with Guy made him switch sides in the end.
Harley Quinn: Clayface goes undercover along with Harley and Ivy as college students. When they are figured out and forced to run on giant hamster wheels, Harley tries to get Clayface to escape, but he is to absorbed into his character to think he could shapeshift back to normal.
Jellystone!: In this series, Quick Draw McGraw appears only in his "El Kabong" persona.
Shayera Hol aka Hawkgirl of Justice League joined the team as an alien spy, but then decided to help them form a counter-offensive, when she found out that her race was really planning to use the Earth as a hyperspace bypass in an interplanetary war, which would destroy it. Feeling guilty of betraying both the Justice League, and her homeworld of Thanagar, she decided to leave the team before they announced their decision on whether she can return.
Legion of Super Heroes (2006) has evil shapeshifter Ron-Kar finding himself sympathizing for real with the good guys, and even willingly helping them, after his Memory Gambit infiltration as Superman is exposed.
The Looney Tunes cartoon Bugs' Bonnets (1956) plays with this idea by casting it in the form of people taking on roles defined by the hats they wear — and then throwing Bugs Bunny and Elmer Fudd into a landscape littered with hats scattered from a passing truck. How many times — and to what degree — can these two Become The Hat? Needless to say, it gets typically extreme.
In the Season 3 episode "Keep Calm and Flutter On", this happens with Discord of all villains. Princess Celestia charges Fluttershy with redeeming him, and Discord plays along while plotting to exploit Fluttershy's kind nature to ensure his freedom. However, during this, he finds out that she genuinely saw him as a friend and her friendship actually means something to him. The end result is Discord reforming for real rather because he can't bring himself to lose the one genuine friend he'd ever made.
This later happens to Trixie as well in "No Second Prances", when she returns to Ponyville and appears to become friends with Starlight Glimmer, Twilight's new student. As it later turns out, Trixie originally only made friends with Starlight to use her against Twilight by having her choose to help Trixie over Twilight. In doing this, she however bonded with Starlight and formed a genuine friendship with her, so much so that when Starlight runs away in tears after discovering this Trixie is heartbroken as well over losing her first real friend. Twilight is later able to talk to Starlight and get her to forgive Trixie for her deceit and become friends for real.
In "Fake It 'Til You Make It", after Rarity asks Fluttershy to look after her boutique in Manehattan while she and her assistants are occupied with a fashion show, Fluttershy creates and acts out three personas to help herself in interacting with Rarity's numerous and hard-to-please costumers. However, she soon becomes so immersed in each of the characters that she stops acting like herself altogether, essentially splitting into three separate people depending on which mask she's wearing at a given time, each of them rude and abrasive in a different way.
Ready Jet Go!: Implied. As shown in "Holidays in Boxwood Terrace", Mitchell fakes his jerk attitude to hide his loneliness and social insecurity. Even after he befriends the other kids in this episode, he still acts like a jerkass in some episodes of season 2, although he's mellowed out a lot more. Since he is shown acting rudely towards the other kids in many episodes of season 1, it is implied that he's been hiding behind his jerk mask for so long, that it's become a part of his personality, and its something that he can't shake off, at least for the time being.
Mayor Jones from Scooby-Doo! Mystery Incorporated turns out to not be Fred’s real dad. He took baby Fred as a hostage to keep his real parents from returning to Crystal Cove. Over the years, he grew to love Fred as if he were his own child. This is touched upon in the first season finale as Mayor Jones, disguised as the Freak of Crystal Cove, saves Fred from falling off a cliff.
The Sheep in the Big City episode "Fleeced to Meet You" had the X Agent pretend to be Sheep's friend in order to manipulate him into getting captured by the top secret military organization planning to use him in a sheep-powered ray gun. In the end, X Agent finds that he really does like Sheep and ends up helping Sheep escape.
In "The Principal and the Pauper", it's revealed Seymour Skinner is actually Armin Tamzarian. He served with the real Seymour Skinner in Vietnam and took over Skinner's identity when he was apparently killed. Twenty years later, the real Skinner shows up in Springfield to reclaim his identity. But the townspeople decide they prefer to keep the Skinner they're used to. The real Skinner is banished from town, Tamzarian is put back in Skinner's identity, and it's ordered that nobody will ever mention this incident again. Well, they do when it's either funny or to shut Skinner up.
In "The Last Temptation of Homer", Homer's guardian angel assumes a different form, first choosing Sir Isaac Newton as someone Homer would recognize and revere, then reluctantly changing to Colonel Klink from Hogan's Heroes when Homer has no clue who Isaac Newton is. When Homer informs him Kinch had a radio in the coffee pot, the angel reacts with genuine alarm.
In "Donnie Fatso", Homer goes undercover to investigate Fat Tony, since he's been sentenced to ten years for trying to bribe a city official and will get a reduced sentence if he does the FBI that particular favor. However, he eventually grows to sympathize Fat Tony and eventually saves him from being shot, though he dies from a heart attack anyway and he is later replaced by a character whose essentially a duplicate of him, though he's fit instead of fat at first.
Cartman fakes having Hollywood Tourette's in order to have fun with his usual language habits, only garnering sympathy rather than derision from authority figures. He forms a plot involving this to say antisemitic things on Dateline, but by that point he had spent so much time not filtering what he says that he unconsciously began blurting out personal secrets such as "I'm making all of this up!", "My cousin and I touched each other's wieners!" and "I wet the bed!"
In "Butters' Bottom Bitch", Officer Yates assigns an undercover agent for a series of prostitution busts: himself. During the operations, he makes his arrests after performing the sex act, each one becoming more and more elaborate, to the point of gangbanging a college fraternity. He even marries the Big Bad pimp at the end of the episode, living with him for months before finally deciding to place him under arrest.
In "Tweek X Craig", Tweek and Craig get depicted as lovers in Yaoi art. They are then Mistaken for Gay, and to put an end to the rumors, pretend to "break up". After the community gets sad, they pretend to get back together for the sake of everyone else. Later episodes and Word of God however reveal that they eventually did become a genuine couple.
Strawberry Shortcake: Happens to Sour Grapes in the 2003 episode "Everybody Dance". In the Purple Pieman's latest attempt at taking over Strawberryland by robbing them of their crops, Sour takes advantage of Strawberry and her friends' love of dancing and opens a fake dance studio and pretends to be the instructor to distract them from his plan. However, teaching them long enough causes her to realize how amazing their dancing is, that she finds herself unable to betray them. Once The Masquerade comes off and Strawberry encourages her to follow the advice in her heart, she begins a Heel–Face Revolving Door.
The kids in Star Trek: Prodigy initially pretend to be Starfleet cadets in order to trick Hologram Janeway into letting them continue to use the Protostar, the Starfleet vessel which they found. By the end of season 1, they have truly become Starfleet officers, with Dal even offering to make a Heroic Sacrifice to save the Federation.
In Star vs. the Forces of Evil, Star’s ex-boyfriend Tom sends one of his minions to pose as the guidance counsellor of Echo Creek Academy to spy on her. He’s shown in later episodes to still be working as the guidance counsellor despite his cover being blown.
Tom himself goes through this several episodes later. He invites Marco to spend some time with him, but it turns out to be part of his anger management training (spending a certain amount of time with someone he disliked), which Marco is upset by. However, Tom did genuinely enjoy his time with Marco, which leads to the two becoming friends for real.
Terra (in the Animated Adaptation only) really began to feel at home with the team and fell in love with Beast Boy. She tried to compromise by saving him and letting Slade kill the others, and, well, you can guess how it turned out.
The very next episode after that arc has Cyborg infiltrate the H.I.V.E. Academy under the guise of "Stone", in order to find out the "big plan" the H.I.V.E. has in the works. While he is able to successfully resist Brother Blood's mind control, unlike the rest of the students, he at one point shows himself to actually be enjoying himself at the school and only manages to focus himself back on the mission due to Robin's insistence.
Teenage Mutant Ninja Turtles (2003): A villainous version. Ch'rell, the Utrom Shredder, stole the identity and appearance of Oroku Saki, the Tengu Shredder, to gain followers. However, years of going by that name eventually caused him to embrace it as his own and declare himself "the one, true Shredder".
In one of the old Tom and Jerry episodes, a duckling comes to think of Tom as his mother. At first, Tom is only taking advantage of it to prepare to cook the little duckling into stew, but by the time the duckling willing decides to do it, Tom can't bring himself to cook the little guy and saves him. Also one of the few episodes that ends with Tom having a happy ending.
Knock Out of all bots does this in the finale movie of Transformers: Prime, Predacons Rising. While his personality and motives remain virtually unchanged up until the very end of the film, his assistance (however limited) when facing Unicron's undead Predacon army and later show of genuine regret when Optimus dies seem to indicate he's truly changed.
Brock Samson was originally assigned to prevent Rusty Venture from ever activating the ORB and was put under the guise of the Venture family's bodyguard, but after several years of protecting them, he truly began to feel like part of their family, and even purposefully refused to kill Rusty when he discovered the ORB. It's heavily implied that until that episode, Brock didn't know what his real mission was.
Also his predecessor who protected Venture's ancestor. He broke/damaged the ORB to the point it would never work instead of killing him. Leading to the events of the episode.
