"I'm saying... I'm saying I'm an insect who dreamt he was a man and loved it... but now the dream is over, and the insect is awake."After months or years of suffering a Split Personality, Enemy Within, or Super-Powered Evil Side, the character is cured! ...by having the weaker, "sane" personality lose all control over the body to their inner evil. Like the slow erosion of a mountain, Jekyll has succumbed to Hyde's implacable id-like force, leaving nothing but the shell of who they were. This isn't just an identity crisis or something that can be wished away with good intentions, at least not easily. This is the permanent and literal death of a person— or at least a personality. This is especially common if one personality is more dominant than the other, or the "good" personality is subject to Mind Rape or a Heroic B.S.O.D.. Occasionally, a truly strong willed "good" personality can do the takeover— although it's likelier that they'll choose to "merge" or reintegrate with their evil side into a "whole" personality because Good Is Impotent. If the takeover is incomplete, expect to see signs that the original is Fighting from the Inside. Antonym to Split-Personality Merge. When this is induced by outside brainwashing, it may be Brainwashing for the Greater Good.
— Seth Brundle, The Fly (1986)
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- Subverted in Ah! My Goddess. Belldandy's sister, Urd, being half-demon and half-goddess, forcibly has her good and evil halves split apart by Mara, and when they are rejoined, she finds that her demonic side is slowly slipping away, which would eventually result in her becoming a full-blown goddess. However, Keiichi and her sisters refuse to let the Urd they've come to know disappear, so they summon the only person other than the Almighty One (whom they assume won't help them since he would rather Urd become a total goddess) with enough power to safely return Urd to stable demon/angel form—the ruler of all demons and her mother, Hild. It works, but they accidentally end up convincing Hild to leave a portion of herself behind on Earth to torment them along with Mara.
- Subverted in Angel Beats!, where Tenshi manages to win out against dozens, if not hundreds of murderous versions of herself after all of them recombine into one person. Given her exhausted state when it happened, and Key's tendency to Kick the Dog, it was a close call.
- A variation occurs in Elfen Lied as the good personality takes over the evil (if tragic and even pitiful) one but neither personality is okay with the omnicidal maniac side taking over at the end of the manga, leading to a shoot the dog moment from Kouta.
- In Animerica, this occurs to Kiyone, explaining his Magnificent Bastard actions in Season 2. The "evil" side attempts to do this again in the beginning of Season 3, but thankfully it gets destroyed for good this time.
- Knives Millions's short transition from a hugely caring and even oversensitive cute boy to a Woobie who hides a lot of anguish and anger management issues from his loved ones to the friggin' biggest homicidal psycho in Gunsmoke's short history and the responsible of what's probably the biggest genocide in human history, period. The anime arguably oversimplifies his transformation and motivations, making his Freudian Excuse quite ludicrous.
- The manga also suggests that Legato Bluesummers' original personality may have been pretty ordinary and that he used to have normal human needs, but that it soon got twisted beyond recognition by years of horrifying abuse in a small town plagued by criminality (and pedophiles) in the middle of nowhere-in-Mordor and not even having a name, parents, or a past worth mentioning in his view.
- In Saint Seiya, the Big Bad of the first major plot arc is Saga, Gemini Gold Saint, a saintly (forgive the pun) warrior in Athena's service, whose Split Personality is thoroughly and irredeemably evil. Naturally, it takes over for good, which results in the Sanctuary War, although Saga's good side still shows occasionally (if only to have an Heroic B.S.O.D. at his own actions.)
- This is why Moka never takes off the rosary herself in Rosario + Vampire: the outer Moka would be replaced by the inner Moka forever. This doesn't stop her from trying it anyway.
- Marik and Dark Marik from Yu-Gi-Oh!. The split personality was born when Marik's father carved his back. The pain was so severe that Marik created a second masochistic personality to cope with it. Dark Marik took control to kill his father a year later and intended to do away with the rest of the family, but he retreated back into Marik's subconscious due to his Morality Chain adoptive brother, Rishid (Odion in the anime dub). When Rishid falls unconscious, Dark Marik takes control and nearly succeeds in killing Marik for ownership of his body.
- Bleach: Hollow transformations consist of the original personality being largely destroyed in favour of something created from raw instinct. The effect is permanent; even if a hollow can resist the effect (such as Sora), it's only a temporary measure at best. The exception is Ichigo who did eventually learn how to control his hollow power and it's eventually revealed to be the basis for his shinigami power and his zanpakutou's sealed form.
- Goes the less common direction for Riff in Count Cain, who was given a nice personality in order to gain Cain's trust, which then faces off, and wins, against the original evil one.
- Pretty Sammy quotes this trope to Misao which it encourages her to help her in getting rid of Ramia's evil influence over her.
Even if you stay as Pixy Misa forever, I'll still really love you, Misao!
- In Psyren when Amamiya is shot Abyss, her other personality created from her suppressed emotions takes over momentarily.
- Played with in Samurai Deeper Kyo. In the manga version, Demon Eyes Kyo is a legendary killer whose mind has been sealed inside the body of Mibu Kyoshiro, but occasionally rises to the surface. In the anime version, Demon Eyes Kyo is the dark side of Kyo's personality that escaped and became an Enemy Without, then was reabsorbed back into Kyo. In both versions, Kyo eventually assumes full-time control of Kyoshiro's body.
- Although Naraku already dominates Onigumo, he plans on removing his heart from him since his love for Kikyo prevents him from hurting her.
- A more classic example comes from Inuyasha himself: whenever in the presence of a powerful demonic aura and/or separated from his sword Tessaiga, his demon blood takes him over and he transforms into his fully demonic form, then proceeds to wantonly murder anyone nearby. It takes an increasingly large amount of effort to bring him back to normal each time.
- Fullmetal Alchemist:
- Bradley's body's original owner was bound to a Philospher's Stone and waged a war with the various personalities trapped inside the Stone until the current Bradley became dominant. Even he's not sure whether he's the original test subject or some other personality.
- Averted with Ling/Greed, which started off this way but ended up as more a case of Symbiotic Possession.
- Shiro in Deadman Wonderland seems to have had her violent side take over. Chapter 55, however, reveals that this is Averted, as her supposed Split Personality never existed in the first place. She is incredibly jealous of Ganta for being able to live a comfortable life she never had as a result of being his replacement and was doing everything in her power to make sure he was strong enough to kill her.
- In W-Change!!, the heroine is a sweet airheaded girl who has an incredibly violent persona that surfaces whenever she falls unconscious. Halfway through the series, her "dark side" took over as her main personality.
- In Frank Miller's Batman: The Dark Knight Returns, Harvey Dent has received surgery to repair his face's damaged half, but it has the opposite effect on his mind - Two-Face is now entirely in control.
- There's a Spider-Man arc involving Symbiote knockoffs. Venom, of course, always refers to himself as 'We' (as in, Eddie Brock and his Symbiote), so when one of the symbiotes stops talking in plural, Spidey knows that she's all gone - the Symbiote has taken over her mind. An interesting conclusion of this is that the very thing that makes Venom sound like a raving lunatic is actually an indication of his remaining sanity - or even a psychic crutch necessary for him to retain his identity.
- While it wasn't made as big a deal of as the animated version, it used to be that the Goblin Serum gave Norman Osborn a Split Personality, and would periodically forget he had a Superpowered Evil Side and go back to being an industrialist. Since he came Back from the Dead, it seems to be accepted that he's the Goblin all the time. Though during his time on Thunderbolts and Dark Reign, it seems the split personality explanation is back. Subverted in that Osborn is still an evil jerk, the Goblin is just his darker side. At the end of "Goblin War", the Goblin formula is flushed from his system, and he declares that Spider-Man has never faced a Green Goblin who's sane before...
- What caused Brainwave's initial Face–Heel Turn after the end of Infinity, Inc. About fifteen years later, the new personality got possessed by a ''third'', also villainous, personality. Eventually, when the third personality was defeated, it was heavily implied that the third personality ate the second one. In any case, he got better.
- Inverted, to some extent, with the Hulk's son Skaar, where the weaker, more vulnerable personality ('puny' Skaar) has recently managed to escape Skaar's suppression of him in their shared mind.
- Betty Ross was in constant risk of this when she was Red She-Hulk.
- During the Spider-Man storyline The Gauntlet, Curt Connors' worst fears are realized when he loses a battle of wills with the Lizard part of his psyche. The Lizard kills and eats Curt's son Billy, and "Curt" essentially dies due to the trauma, leaving only The Lizard. A later story reverses this Spider-Man manages to bring Curt's body back, but doesn't realise it's still the Lizard's mind. Then the Lizard reverts to his usual form, but this restores Curt's mind. Curt keeps this quiet because he feels he deserves to be locked up.
- This was Bloody Mary/Typhoid Mary's (a villainess most often found in Daredevil) entire schtick. She had rather impressive psychic and telekinetic powers, but she also had a horrible case of multiple personality disorder; namely, at least nine of them. Two of them (the aforementioned Bloody/Typhoid Marys) tended to take over more often than not, and there have been at least two instances where one or both have "permanently" taken over only for later events to unlock her original (non-powered) personality once more.
- Happened to Ultimate Moon Knight. Doubles as a case of Becoming the Mask, since the personality that took over was created specifically to be more evil and violent.
- In Golden Age DC comics, Priscilla Rich's jealousy and envy of Wonder Woman caused her to spawn a second personality. As the Cheetah, she became a recurrent foe in the Sensation Comics and Wonder Woman series.
- Pony POV Series:
- Discord originally entered the mortal world as an innocent version of himself named Dissy who had none of his evil self's memories. Sadly, Discord's original persona still existed and eventually began to awake until it finally devoured Dissy and began his thousand year reign. It's mentioned in-universe this happening was unique to Discord, as most deities instead have a Split-Personality Merge in situations such as this.
- A benevolent version happens with Minuette, who's actually the Master using a fob watch. While her evil persona spends the arc attempting this trope, eventually Minuette manages to destroy the Master by feeding his fob watch to the Blank Wolf, allowing her to take his place fully.
- The dark side of Socrates attempts this in Calvin and Hobbes: The Series, as his transmitter chip has fused with his mind, allowing the dark version to try and take over the land inside his head. The protagonists stop him, of course.
Films — Live-Action
- In the remake The Fly (1986) Scientist Seth Brundle slowly transforms into a pathetic and diseased human-fly hybrid after accidentally fusing with said-insect in a teleporting experiment. At first, the deformities were purely physical, as his human flesh warped and decayed into a "cocoon" under which the monster grew. Sadly, he also transformed on a mental level into an instinct based animal, unbound by compassion and morality. The love of Veronica, our heroine, was sadly not enough to stop his predictions from coming true...
- Averted in the sequel The Fly II with Brundle and Veronica's son Martin. The murderous rampage against his oppressors is all him. They are bad enough that this isn't a Moral Event Horizon for Martin.
- The VERY heavily fictionalised film of "The Boston Strangler" implies something like this at the end. The killer, Albert De Salvo, has been diagnosed with Multiple Personality Disorder (the real life De Salvo was never even suspected of having this condition,) and the film ends with him apparently having gone permanently catatonic after re-enacting one of the murders under the influence of his murderous side, and with no sign of the gentle family man left.
- In the "Ventriloquist's Story" in Dead of Night, ventriloquist Maxwell Frere (Michael Redgrave) smashes up his puppet/Demonic Dummy "Hugo" (who, it is strongly implied, channels Maxwell's own Split Personality) after "Hugo" tauntingly threatens to join Maxwell's rival ventriloquist. Maxwell is placed into a mental institution and goes into a catatonic state until his doctors bring in the rival ventriloquist to try and give him a jolt. Upon seeing the rival, Maxwell smiles and opens his mouth, but the voice that comes out of his throat (his lips remaining unmoving) is that of "Hugo".
- This happened to Dr. Jekyll at the end of his strange case. Luckily for Victorian England, Jekyll saw this coming, locked himself up before changing completely, and ultimately committing suicide.
- In a rare case of the good side taking over (with a little help), from Gene Wolfe's story "The Death of Doctor Island", the psychotic teenager William, whose brain has been surgically divided between the left and right hemispheres, is deliberately subjected to a devastating trauma which leaves him catatonic. This allows his previously helpless right-brain personality, the calm and placid "Kenneth", to take control of his body.
- Artemis Fowl:
- Happens to one of the bad guys in Shade's Children: When the titular Knight Templar Virtual Ghost uploads himself into a supercomputer, his conscience becomes personified in Robert Ingman, who is, coincidentally, Shade's original identity. As with the trope, Robert eventually destroys his dark side and helps the protagonists banish the local Dimension Lords. Too bad the other rule about redemption is played quite straight.
- In The Lord of the Rings, the character Gollum's darker side of his personality ultimately ends up taking control over his kinder side.
- Came this close to happening to Tahiri/Riina from the Star Wars: New Jedi Order series. Riina was not "evil", per se- though extremely messed up, she had a Pet the Dog in one of the few times she actually did manage to seize control of their body, and the merge helped Tahiri regain her sanity largely because each compensated for the other's issues (Riina's acceptence of pain and death helped Tahiri get past her emotional fragility following her boyfriend's death, while Tahiri's moral center held back Riina's more violent urges).
- In The Pilo Family Circus, this happens to every single clown employed by the circus, due to prolonged use of the magical facepaint they wear: it takes around two years of usage for the new personality to completely merge with the clown's brain, but since the facepaint also grants the user superhuman strength, a newly-recruited clown has to wear it just to survive the early months at the circus, and by then, the clown's addicted. Jamie, the novel's protagonist, only just manages to avoid this fate.
- This happened to a teenager named Saxon Hyde at the beginning of Michael Slade's Ghoul. That's especially unfortunate, because Saxon was the only one of this young man's personalities that wasn't a serial killer.
- The first half of the Dragonlance: The New Adventures series consists of an evil wizard trying to engineer one of these. He implanted the preserved spirit of a powerful evil sorceress in one of his mindwiped servants to try to access her magical knowledge once she took over the servant. Needless to say, the sorceress is rather pissed when she does take over.
- In Zen and the Art of Motorcycle Maintenance the Narrator first tells us that Phaedrus has been killed by several thousand volts to the head. However, throughout the Chautauquas, it becomes clear that Phaedrus is alive and kicking and trying to gain control. Slightly different from the others, as it's the narrator's personality, the sane personality, that is the real takeover.
- In Stephen King's short story "Secret Window, Secret Garden," Mort Rainey's alter ego John Shooter claims Rainey "took the coward's way out". He briefly reverts to Rainey, but only after being shot.
- Robert Ludlum's The Bourne Supremacy features the Jason Bourne persona forcibly suppressing the civillian identity, David Webb , whenever they need to focus on doing something that requires his particular skillset or way of thinking. Later in the book, Bourne completely takes over as 'Delta', the insane version of David Webb that led Medusa into battles in Vietnam, in order to violently break into the sterile house. Fortunately Marie is there to bring Webb back to the surface.
"David Webb had disappeared, only Jason Bourne remained. Yet he was both more and less the hunter of Carlos the Jackal. He was Delta the predator, the animal wanting only vengeance for a priceless part of his life that had been taken from him once again"
- In Fight Club, the Narrator spends the story slowly succumbing to his intense, charismatic dissociated identity Tyler Durden. Ultimately, the Narrator is Driven to Suicide in order to stop him.
- Played with in Farscape. Thanks to Scorpius' neuro chip, Scorpius' "neural clone" gets stronger and stronger within Crichton over the course of the second season... until taking over completely in the finale. Even after surgery removes the chip itself, the neural clone, "Harvey", never really disappears.
- Once the chip is removed though Harvey loses any power he had and is basically trapped in John's head forever, with John able to shut him up whenever he wishes. The best Harvey can do to John is be mildly irritating - unless his life is in danger, in which case, Harvey can muster up just enough power to be dangerous. In the Peacekeeper Wars mini-series Harvey finally dies for good when the wormhole knowledge is deleted from John's brain.
- Basically what happened to Talia in Babylon 5. There was also a rogue telepath in one episode that goes through this.
- Born vampires from Young Dracula all go through an attempt at this when get their full vampire status. How strong-willed they are seems to determine how much of their original personality is left afterward.
- Implied to have happened at the end of a Married... with Children episode in which Bud's "cool" personality took over. It had absolutely no visible impact on future episodes (though perhaps that's the joke; Bud's so uncool that even his cool side is uncool).
- In an episode of Criminal Minds, a young man's murderous and until-then unknown alter-ego permanently takes over his body, in an attempt to protect him. In a twist, the alter-ego that took over was female.
Dr. Reid: I am looking for Adam.Amanda: Just because you caught me doesn't mean you'll find him. You're not that smart.
- An episode of Stargate SG-1 had Daniel controlled by several different personalities that got in his head.
- Stargate Atlantis has an episode where Rodney and a (female) Marine wind up sharing his body. They each fight over control of the body, until it can't take their fighting anymore: if one of them doesn't give up and willingly disappear, both will die.
- United States of Tara: Alice, the "housewife" personality, reveals that she's jockeying to be the emergent personality if Tara ever resumes therapy. This was followed by Bryce, Tara's alter based on her childhood abuser, revealing that he wants to "kill" Tara.
- Jekyll: When Klein & Utterson finally manage to capture Dr. Jackman, they put him into a device that deletes one of the two personalities. Unfortunately for Jackman's wife, Hyde is the surviving personality. However, when Mrs Jackman and her children are captured due to Hyde's immaturity, he resurrects his dead alter-ego and merges with him, mixing Hyde's incredible strength with Jackman's maturity.
- This happened repeatedly to Nikki on Heroes when her Superpowered Evil Side decided to start acting up.
- This happens to Willow when Tara dies.
- After Spike regains his soul, he intermittently becomes evil again after The First Evil prompts him with a Victorian folksong.
- In season 8, it's shown Oz came very close to going down this road willingly. He had been trying to deal with his werewolf side for a relatively long time, only to learn that whatever he tried was pointless and whatever ground he had gained before was lost. Eventually giving in and simply being done with it all started to look very tempting. It's never explicitly stated why he didn't go through with it, but his words "But I didn't" are coupled with an image of Bayarmaa, his future wife and mother of his son.
- This happens to Angel whenever Angelus is unleashed.
- In Terminator: The Sarah Connor Chronicles, Cameron experienced a case of this when her processors glitched due to combat damage, and Cameron slipped into an alternate personality mode that thought it was a woman named Allison Young, who was a resistance fighter in the future who was connected to the future John Connor, whom Cameron interrogated, mimicked the appearance and personality of, and subsequently killed.
- A positive example occurs on The Twilight Zone (1959). In the episode "Nervous Man In A Four Dollar Room", a small-time thug (Joe Mantell) is ordered to kill someone for the first time in his life. His long buried conscience refuses to go along with committing murder and takes over as the dominant personality.
- In one episode of Tales from the Crypt a lonely man's only companion is his own split personality. When the man starts dating a therapist, said split personality is afraid that she will destroy him and tries to goad the man into killing her. When the guy refuses, his other half decides to "kill" him and take over his life. In the end, the more assertive personality has cowed his former boss and is on the fast track to becoming an executive and is married to the therapist.
- This is extremely common on Supernatural, due to the prevalence of demonic possessions and sympathetic monsters who want to retain their humanity but are incapable of controlling their predatory instincts. Memorable non-possession examples include Lenore and God-mode Castiel, after he ingests the Leviathan. Throw in manly tears, and you could almost turn this into a drinking game.
- Warehouse 13: "The Ones You Love" reveals that the "Brother Adrian" that Artie's been dealing with all season is a hallucinatory manifestation of an increasingly powerful Enemy Within. Just as Artie realizes this, it grows powerful enough to assume control completely.
- Doctor Who: The Eleventh Doctor has to fend off the Cyber Planner that calls itself Mr. Clever when it attempts to take over his mind. Seeing Matt Smith Acting for Two in a Sméagol/Gollum type fight is equal parts awesome and hilarious, with a touch of bone-chilling sinister thrown in by the the episode's author.
- In the live-action drama version of Death Note, Mello starts off as a darker split personality of Near, kept mostly in check. Towards the end, Near collapses, and Mello takes over, complete with Evil Costume Switch.
- In the "One Last Prayer" episode of HBO's 80s anthology The Hitchhiker, a pretty and talented singer called Miranda invents an image for herself guaranteed to succeed, but finds it starting to take over. She fights back, but The Bad Girl Wins.
- BIONICLE: In one of the alternate universe Takanuva stumbles through, the alternate Makuta Teridax absorbs Matoro, who failed in his mission to save Mata Nui in this universe. When Makuta absorb other beings, they normally absorb their bodies and minds, but Matoro fights back, killing himself and Teridax, becoming the hero he was destined to be.
- Along with wrestling as himself, Mick Foley also wrestled under the personas known as "The Three Faces of Foley", which consisting of Cactus Jack, Mankind, and Dude Love. No one ever knew when he switch personas, resulting in one hell of a Wham Episode when he let Catcus Jack take over to fight Triple H in 2000.
- Black Serpent and Timothy Krane got to Bill Black in Fringe Pro Wrestling and manipulated him into suppressing his split personality Will White.
- The Harrowed from Deadlands are constantly in danger of this, since they owe their very existence to the demons possessing them. Except Stone. He's already such an evil, cruel, monstrous asshole that his Manitou just hides in the back of his head and tries not to call attention to itself.
- What happens to Experiments in Bleak World if they get too inhumane for the voices to stomach or are a little to liberal with their magic.
- In Twisted Metal: Head-On, Marcus Kane gives into Needles Kane, aka Sweet Tooth. Interestingly, however, it's not a complete takeover, but rather they seem to be working together, thereby making Dark Tooth and Tower Tooth (the two cars they drive together) the strongest in the game.
- The bad ending of Soul Nomad & the World Eaters involve this, with Gig using your greed to destroy the main character's soul and taking over his/her body. The 'bad' ending of the Demon Path reverses the roles, with the main character destroying Gig instead.
- Both the good and the evil ending of The Suffering: Ties That Bind results in either Torque or Blackmore wiping the other personality out completely.
- The bad ending of Manhunt 2- achieved by killing people as gruesomely as you can - has Leo killing off Daniel's personality and becoming the sole resident of his body.
- Near the end of Planescape: Torment you get trapped in a place where you encounter three of your previous "incarnations". One wants to take you over so and another simply wants to destroy you. If you manage to forcibly take over the other two or get them to merge with you, you will gain their memories (and a ton of XP). If you fail, you have to destroy them and their memories are lost forever. The third takes no convincing to get him to merge with you and is more than happy to.
- Vampire: The Masquerade – Bloodlines has a scene where, after being led along by the two, you finally confront Jeanette and Therese Voermann — wait, make that Tourette Voermann. One half of her face is done up in Therese's professional businesswoman style, while the other half is done up in Jeanette's slutty schoolgirl style, and the two sides speak in turns about wanting to kill the other. Depending on the dialogue you choose, either Jeanette kills Therese, Therese kills Jeanette, or the two personalities decide to put aside their differences and coexist.
- Done very strangely in the Warcraft series; Arthas was a paladin who is corrupted by the Lich King, becomes his champion, then later merges with him, but then Arthas takes over the Lich King, an entity of godlike mental power. A dark lord taken over by another dark lord who is later revealed to be slightly less evil than everyone thought him to be when they became one dark lord.
- One of the main plot points of Riku's story in Kingdom Hearts: Chain of Memories and its remake is that Riku is fighting off the last of Ansem's darkness within his Heart. Several times he almost falls to it, and once he actually does, however how it happens depends on the version. In the original, after completely dominating Lexaeus in their fight, the latter blows himself up in an attempt to drag the latter down into the Darkness. However, in the nick of time, he is able to resist. In the remake, after a stalemate battle, Riku lunges at Lexaeus to finish him off, only to be backhanded into the ceiling and passing out. Unconscious Riku's body is possessed by Ansem who then kills Lexaeus in one hit before Mickey appears and frees Riku.
- Inazuma Eleven: Fubuki Shiro, who is taken over by Atsuya, his inner mind's high ego little brother.
- A positive example can be found in Deadly Premonition, where upon being traumatized and locked in the White Room by Forrest Kaysen, Francis Zach Morgan develops the personality of Francis York Morgan, who takes dominant control in order to protect Zach. At the endgame, Zach is given back control for the final confrontation with Kaysen.
- In Mortal Kombat 9 a positive example appears in Ermac's Arcade Ladder ending. The soul of King Jerrod, Kitana's father and Sindel's husband, eventually becomes dominant in Ermac and becomes Edenia's protector again.
- Super Robot Wars Alpha 3: Subverted When Cobray Gordon was formed from the fusion of Ayin and Ingram, Ingram tries to take over Ayin's body but ultimately realizes that he himself is being absorbed by Ayin
- In The Elder Scrolls verse, the Daedric Prince of Order Jyggalag was cursed by the other Princes with this becoming the Prince of Madness Sheogorath. He can only briefly become himself again every few thousand years, and never long enough to permanently restore his realm. "Killing" and replacing him in Shivering Isles frees him to wander Oblivion again.
- In Fallout: New Vegas, Lily's aggressive alternate personality, Leo, who usually appears to her as a completely separate entity standing beside her, will take over her body when she goes down to 1/4 of her HP, making her unresponsive to any command. Witnessing this triggers her companion quest where you discover that she's only been taking half-dosages of her meds. You can convince her to keep doing what she's doing, take the full dosage to suppress Leo completely at the cost of making her weaker in combat, or stop taking them altogether, which causes Leo to come out at 1/2 HP but makes her much stronger in combat. Similarly, Dog/God in Dead Money may have one of his personalities destroy the other, or merge the two.
- In Counterfeit Monkey, this doesn't happen all the way but there are still Fridge Horror implications of it after Alex and Andra (who started out as separate people, but voluntarily fused together as one person to make escaping the authorities easier) are forced to decide whether to betray Alex's father or Andra's boyfriend. Immediately after they make their decision, the personality who got the upper hand in the decision suffers a brief bout of dizziness and from then on becomes the semi-dominant personality. It's done subtly enough that the player might not notice until the very end of the game (when it's revealed that they no longer have equal control of their body and hence cannot be separated), but examining the PC at any point afterwards will reveal that either Alex or Andra feel as if their body has become more the other personality's than their own and that they're more of a hanger-on than a co-partner now, and there's also a subtle increase in pronoun usage for the dominant personality (a greater number of "I"s from Alex, or a greater number of "you"s from Andra).
- Averted in American McGee's Alice. Alice's Battle in the Center of the Mind with The Red Queen would have determined which of her personalities would be dominant and which would be cast down and forgotten.
- In Mystery Trackers: The Void Marius Void's criminally-inclined "brother" Sirius takes over his body after killing his psychiatrist, who'd been supplying drugs to suppress the transformation.
- This is the major twist in the freeware Visual Novel Ori Ochi Onoe. The protagonist used to be in love with the sweet and gentle Ori, but Ori turned out to be a split personality of the more violent and temperamental Ochi with the two personalities referring to each other as "sisters" and leading separate lives. Unfortunately, a later eye operation destroyed the Ori personality and left just the Ochi personality who the protagonist subsequently entered a very complicated and twisted relationship with. One of the game's endings has Ori regain control after the protagonist makes it clear that he loves only her, and another ending has the two personalities merge to create a more complete Ochi.
- Umineko: When They Cry: The main villain of the third arc is Eva, who has a sort of Imaginary Friend and Literal Split Personality that looks like she did as a child. When Eva finds the gold, her Split Personality becomes Eva-Beatrice, and it's nicely proven that With Great Power Comes Great Insanity. Over the rest of the arc, Eva's "human side" breaks down more and more, and she spends a lot of it locked in her room with a fever. But after George and Hideyoshi are killed, she snaps into outright Ax-Crazy-ness, starts using Evatrice's Catch Phrase, and shoots Battler.
- A curious example in Red vs. Blue: Reconstruction - when an AI is implanted in a character, the effect is described as being "of the same mind", where the two entities share thoughts. Though the host is usually able to maintain his or her identity (even if free will is lost), Agent Maine (better known as the Meta) degenerated into a mindless husk after playing host to 7 different AIs at once and stayed that way even when the AIs were removed. Of particular note is the fact that all 7 AIs were Literal Split Personalities of another AI, the Alpha.
- Whateley Universe: Sara Waite is really a Great Old One who is supposed to evolve into The Kellith, a being who will wipe the earth of humanity and re-populate it with her spawn. She ends up having a fight to the death with The Kellith in a Journey to the Center of the Mind.
- Done in a masterfully nightmarish way in Marble Hornets. In Entry #61, we're treated to a video of the hooded masked man stealing Tim's medication while Tim is in the bathroom during a coughing fit. After Hoody hides, Tim stumbles into the room and undergoes a disturbingly realistic seizure, then jerkily climbs to his feet and absconds, all with the heavy implication that his other personality, the original masked man, is back in the driver's seat. Amongst the evidence that Masky is in control is his pronounced limp- after his leg was previously broken, he'd been limping up to his last chronological appearance in the series.
- Homestuck: Calliope, a sweet and genuinely kind girl, shares a body with Caliborn, a barely restrained sociopath. At the end of Act 6 Act 3, Caliborn becomes not so restrained, escapes from his confines, and starts a session on his own, taking over their body completely and burying Calliope in the process. However, some characters believe that she may not be entirely dead and that in fact finding her might be the key to defeating Lord English once and for all. The author mocks Caliborn for doing this, since he stunted his own Character Development by averting the Split-Personality Merge that Cherubs normally go through.
- Norman Osborn undergoes this in Spider-Man: The Animated Series.
Green Goblin: (to Harry Osborn) Your whining simp of a father doesn't exist anymore. I am the ultimate evolution of Norman Osborn!
- X-Men: Evolution, episode Sins of the Son. Charles Xavier discovers he has a son in Scotland, David Haller, and goes to meet him, only for two other boys to enter the fray as well. These three boys (David, Ian, and the evil Lucas) are all parts of the same being. Xavier tries to help expunge Lucas, but ends up locking away David, forever losing his son as Lucas goes off, never to be seen again (as the series was cancelled before this story could continue).
- In South Park, at the end of "City Sushi", the police allow Dr. Janus to keep on thinking he's Lu Kim, since Lu Kim owns the only Asian restaurant in town after City Sushi was destroyed.
- In Total Drama All-Stars Mike was in the previous season was established as having several different personalities. In the episode "Evil Dread" the previously unknown personality Mal is set free when Mike is hit in the head with a shovel, albiet slightly, as he switches in and out at random. Some episodes later Mike attempts to seal him away again by hitting his head on a large rock, but it only serves to imprison Mike in his own mind and give Mal free reign.
- In the Ben 10: Omniverse episode "Max's Monster", Max's Evil Former Friend Phil comes back after a long stint in the Negative Zone mutated and insane after he was used as a test subject for the Nemetrix. He frequently transforms into a savage energy eating monster with a mind of its own and begs the heroes to help him. Ben is suspicious but Max and Rook are willing to try. Ben is Properly Paranoid, since "Phil" soon admits that "there hasn't been a Phil in this body for years". The monster personality has been in control the entire time, and Phil is long gone.
- In The Amazing World of Gumball episode "The Name", when Gumball's discovery of his first name being Zach results in "Zach" becoming his own person, the latter tries to alter the former's memories to erase him from existence.
- Adventure Time has this happen to Simon Petrikov, as documented by his tapes. Although the moment in which he fully became the Ice King has yet to be shown onscreen, the tapes show him increasingly slipping in and out of his current persona's mannerisms; while the later episode "Simon and Marcy" shows him initially resisting this, but the end of the episode makes it clear that he's losing himself and that this trope will soon occur.
- The Avengers: Earth's Mightiest Heroes! has a rare consensual example — Bruce Banner lets the Hulk take over his body as long as the Hulk works alongside the Avengers as a hero. Eventually, Bruce is allowed to have control for one day a month.
- An episode of the dramatized court-case anthology series The Judge dealt with a female dissociative identity disorder patient who, in the episode's surprise twist, turned out to be the victim of her psychiatrist, who was having an affair with her Femme Fatale persona and plotting to destroy her original personality so the two of them could be together. While the script might've involved some dramatic exaggeration, there are real-life cases of secondary personalities in DID cases plotting to kill their primary selves, without recognizing that if they're successful, they'll die too.